docs: add the Plan 9 assembly case and real-use note to the README

CHANGELOG.md

@@ -40,6 +40,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   states the commit trailer form, the one-logical-change rule and the
   licence header rule.  The repository's own assembly (the `verify`
   trampolines and the test kernels) is in `gasm fmt` canonical form.
+- **The README states the project's purpose and status.**  It opens with
+  a warning that the tool is an experiment under active development,
+  version 0.x.x, free to change without warning, with 1.0.0 far off,
+  and already in active use on real assembly work.  It describes both
+  goals (tooling for Plan 9 assembly, and Plan 9 assembly outside the
+  Go toolchain), argues the case for the syntax in a new Why Plan 9
+  assembly section, and carries a Direction section: extended
+  instruction support, full GOOBJ and ELF compilation, Linux and
+  FreeBSD, and the four architectures.
 
 ### Fixed
 

README.md

@@ -1,13 +1,63 @@
-# gasm-devkit
+# Plan 9 assembly tooling, inside and outside Go
 
-Developer tooling for **GAsm**, Go's built-in Plan 9 assembler.
+> **Warning: this is an experiment.** gasm-devkit is under active
+> development and is not stable. The version is 0.x.x: commands, flags,
+> output formats and behaviour can change without warning at any time.
+> A 1.0.0 release is light years away. Nothing in this document is a
+> stability promise. For all of that, this is not a paper project: gasm
+> is already in active use and is tested on real assembly work.
 
-Go ships an assembler but no tooling for it: there is no syntax highlighting,
-no autocomplete, no linter, no static analyser, no formatter, no standalone
-assembler and no debugger for `.s` files.  Developers write assembly blind,
-validate it by benchmark, and debug it by print statement.  gasm-devkit is the
-missing toolkit: a single, self-contained binary, `gasm`, that brings proper
-developer tooling to Plan 9 assembly on amd64, arm64, riscv64 and loong64.
+**GAsm** is Go's Plan 9 assembler, and Go ships it without tooling:
+there is no formatter, no linter, no static analyser, no standalone
+assembler and no debugger for `.s` files. Developers write assembly
+blind, validate it by benchmark, and debug it by print statement.
+gasm-devkit is the missing toolkit: a single, self-contained binary,
+`gasm`, that serves both purposes.
+
+- **Help develop Plan 9 assembly.** Formatting, linting, disassembly,
+  dynamic verification, a source-level debugger and a language server,
+  for `.s` files in Go programs.
+- **Use Plan 9 assembly outside the Go toolchain.** `gasm asm` encodes
+  on its own, with no Go installation in the loop, and writes raw
+  images, linkable ELF objects with DWARF5 debug sections, or the Go
+  toolchain's own GOOBJ format, which `go build` consumes in place of
+  the toolchain's output.
+
+## Why Plan 9 assembly
+
+Plan 9 assembly is the quiet triumph of the field. One syntax across
+every architecture Go builds for: the same source-first operand order,
+the same four pseudo-registers, the same frame convention, whether the
+target is x86, ARM, RISC-V or LoongArch. Learn it once and you can
+read a kernel on any of them.
+
+Compare the alternatives. Intel syntax and AT&T syntax disagree on the
+one question every instruction answers, which operand is the source
+and which is the destination, so half the world writes it one way,
+half the other, and every assembly programmer carries both in their
+head forever. GNU as settles the argument with directives that switch
+dialects mid-file (`.intel_syntax noprefix`), a percent sign on every
+register and a dollar on every immediate: punctuation that carries
+nothing the operand order did not already say. And the x86 family
+fragments again underneath: NASM is not MASM is not GAS, each with its
+own directive zoo and macro language, so every project picks a dialect
+and every reader learns a different one by accident.
+
+Plan 9 assembly has none of it. Registers are bare names. Memory is
+one notation, `offset(base)`, extended by an index and a scale when
+the instruction needs it. Arguments arrive named and offset-checked:
+`x+0(FP)` is the argument x, on every architecture, and `go vet`
+polices the offsets against the Go prototype.
+
+```text
+AT&T (GNU as):   movq %rax, -16(%rbp)
+Plan 9 (Go):     MOVQ AX, total-16(SP)
+```
+
+The same lines, but only one of them tells you what the number is for.
+The syntax is uppercase, regular and boring, which is the highest
+compliment a language for machine code can earn. gasm-devkit exists
+to give that syntax the tooling it deserves.
 
 ## Features
 
@@ -47,12 +97,11 @@ developer tooling to Plan 9 assembly on amd64, arm64, riscv64 and loong64.
   assembly files byte-for-byte, `gasm profile` shows basic-block structure,
   `gasm audit-instructions` diffs the encoder against the installed toolchain,
   and `gasm scaffold` generates a differential test skeleton for a kernel.
-- **Complete instruction coverage.**  The instruction tables are generated
-  from the Go toolchain's own assembler source, so the toolkit recognises
-  every mnemonic the real assembler accepts; `just gen` refreshes them.
 
 ### Architecture support
 
+Four architectures, the four that matter in practice:
+
 | Architecture | GOARCH      | File suffix  | Instructions recognised                     |
 |--------------|-------------|--------------|---------------------------------------------|
 | AMD64        | `amd64`     | `_amd64.s`   | 1600 + common opcodes + traditional aliases |
@@ -63,9 +112,38 @@ developer tooling to Plan 9 assembly on amd64, arm64, riscv64 and loong64.
 "Common opcodes" are the instructions shared by every architecture (`RET`,
 `JMP`, `NOP`, `CALL`, `TEXT`, `FUNCDATA`, `PCDATA`, ...).  AMD64 additionally
 carries the traditional conditional-jump spellings (`JZ`, `JNZ`, `JA`, `JC`,
-...) that the assembler accepts as aliases.  Regenerating the tables is one
-command (`just gen`) and requires only a Go installation; the committed output
-has no runtime dependency on the toolchain.
+...) that the assembler accepts as aliases.  The tables are generated from
+the Go toolchain's own assembler source (`just gen` refreshes them), so
+every mnemonic the real assembler accepts is recognised; what the encoder
+can emit today is narrower, and a recognised but unencodable instruction is
+reported as an explicit error, never as a wrong byte.
+
+## Direction
+
+The plan, in the order it is being worked:
+
+- **Extended instruction support.**  Two layers. First, encoding
+  coverage for every mnemonic the Go toolchain itself accepts, closed in
+  order of how often real code needs each instruction;
+  `gasm audit-instructions` measures the gap. Second, the larger work:
+  an extended instruction set the toolchain does not know at all. The
+  toolchain-derived tables stay generated and untouched; only the
+  extended instructions are hand-maintained, with their own spellings
+  and encoders, verified by execution on real hardware because the
+  toolchain offers no ground truth to compare against. The gaps exist
+  on every architecture, amd64 included.
+- **Full GOOBJ and ELF compilation.**  The destination is a complete,
+  standalone compilation path: linkable ELF objects for consumers outside
+  Go, and GOOBJ objects that `go build` links directly.  Through GOOBJ, a
+  Go program will be able to use machine instructions that the Go
+  toolchain itself does not support; through ELF, Plan 9 assembly becomes
+  usable outside Go entirely.
+- **Platforms: Linux and FreeBSD.**  Linux is supported today on all four
+  architectures and is where the binary builds.  FreeBSD follows: the
+  JIT's executable-memory mapping and the ptrace debugger layer are the
+  two pieces of porting work.  Other unix systems may follow those two.
+- **Four architectures, no more.**  amd64, arm64, riscv64 and loong64.
+  No others are planned.
 
 ## Install