documentation: Updated CHANGELOG.md to reflect PR #857 for zh_cn.json (Simplified Chinese) update

Author: rbasamoyai

CHANGELOG.md

@@ -7,6 +7,7 @@
 Changed:
 - [1.20.1] Create Big Cannons will not load with the latest release of CBC: Advanced Technologies until an issue on their end is fixed.
   - CBC: Advanced Technologies breaks Big Cartridges and prevents them from firing. Other issues may also be present.
+- [1.21.1] Updated Chinese (Simplified) (zh_cn.json) localization courtesy of pingguomc
 
 Fixed:
 - Fixed NO_DAMAGE munition damage setting not applying to shrapnel (including flak and grapeshot)