docs: changelog for the completeness waves

Assisted-by: GLM 5.3 Flash

CHANGELOG.md

@@ -35,6 +35,25 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   Also fixed on the way: arm64 `CASD`/`CASW` lacked an opcode bit, and
   riscv64 `VSETVLI` with an immediate length now canonicalises to
   `vsetivli` as the toolchain does.
+- **The GOROOT instruction wave, part 2.**  The encoder gains the
+  quad-register AVX-512 families (4FMAPS, 4FNMADD, 4VNNIW, VP4DPWSSD,
+  VP4DPWSSDS) with the register list riding the inverted V'VVVV field,
+  floating-point immediates on the SSE scalar moves and arithmetic
+  (the constant lands in a synthesised read-only pool, a positive zero
+  collapses to XORPS exactly as the toolchain does), accept-and-ignore
+  FUNCDATA and PCDATA, three-operand double shifts, static-symbol
+  operands for the legacy SSE moves, and the pooled 64-bit immediate
+  materialisation on riscv64.  The parser carries bracketed register
+  ranges, index-only VSIB memory operands and bare trailing immediates;
+  macro substitution reaches parameters used with element suffixes
+  (`A.S4`), and `;` separates statements in plain files.
+- **`gasm asm -GOOS`.**  The go_asm.h generator type-checks per target
+  GOOS, so the darwin-only and windows-only runtime files assemble with
+  their own defines; the corpus audit derives the GOOS from the file
+  name.  DATA initialisers accept `$symbol(SB)` values (an absolute
+  relocation at the data field, GOOBJ on all four architectures and ELF
+  on amd64, arm64, riscv64 and loong64), and U+2215 is accepted inside
+  symbol package paths.
 - **The corpus audit measures honestly.**  Files named for Go ports gasm
   does not target (arm, 386, s390x, ...) are no longer attempted for the
   four supported architectures (no supported build compiles them), and