Update changelog

Author: tgoyne

doc/ffms2-changelog.md

@@ -7,6 +7,7 @@
   - avisynth: Use 2.6 RC API and add output support for all new colorspaces (Myrsloik)
   - vapoursource: Fix swapped RGB channels bug introduced in 2.21 (Myrsloik)
   - swscale: Drop pointless and slow bitexact flag from resizer settings (kodabb)
+  - Add support for files with gaps between the audio packets (Plorkyeran)
 
 - 2.21
   - Add missing constants for log levels (Myrsloik)