changelog: mention use of if(@available(...)) in sokol headers

CHANGELOG.md

@@ -129,6 +129,11 @@ See the new [shadows-depthtex-sapp](https://floooh.github.io/sokol-html5/shadows
 
 - bugfixes and under-the-hood changes
  - `sg_begin_pass()` used the wrong framebuffer size when rendering to a mip-level != 0
+ - the Metal backend code started to use the `if (@available(...))` statement
+ to check for runtime-availability of macOS/iOS API features (this caused problems
+ in the sokol-zig bindings with Zig version 0.10.1, this is fixed in the current
+ zig-0.11.0-dev version => I'll merge the zig-0.11.0 branch of the bindings into
+ master a bit early, hopefully zig 0.11.0 isn't too far out)
  - on macOS the Metal backend now creates resources in Shared resource storage mode if
  supported by the device
  - on iOS the Metal backend now supports clamp-to-border-color if possible (depends on