Document Windows ARM32 removal and update platform list

- Remove win_arm from supported platforms in README
- Add last supporting SDK version (10.0.22621) to CHANGELOG
- Clean up platform documentation

Author: kristjanvalur

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Removed
 - **BREAKING**: Dropped Windows ARM32 (win_arm) support
   - Microsoft Windows SDK 10.0.26100.0+ no longer supports 32-bit ARM development
+  - Last SDK version supporting ARM32 was Windows SDK 10.0.22621 (Windows 11 SDK, version 22H2)
   - ARM32 Windows devices (Windows RT) are obsolete
   - ARM64 Windows remains fully supported
 

README.md

@@ -77,7 +77,6 @@ calling convention, plus archive format:
 
  - win_x86 (32 bits)
  - win_x64
- - win_arm (32 bit ARM)
  - win_arm64 (64 bit ARM)
  - sysv_i386 (linux)
  - sysv_amd64 (linux)