update changelog

CHANGELOG.md

@@ -3,6 +3,8 @@
 - **16-Jan-2022**:
   - sokol_audio.h android: https://github.com/floooh/sokol/pull/747 has been merged
     which adds a couple more error checks at OpenSLES startup.
+  - sokol_gfx.h: support for half-float vertex formats has been added via
+    PR https://github.com/floooh/sokol/pull/745
 
 - **15-Jan-2022**: two bugfixes in sokol_app.h and sokol_gfx.h:
   - sokol_app.h x11: Mouse button events now always return valid mouse