Add changelog/credits entries since the retint fix is quite old

Author: Metadorius

CREDITS.md

@@ -51,6 +51,7 @@ This page lists all the individual contributions to the project by their author.
   - Warhead activation target health thresholds
   - MP saves support for quicksave command and savegame trigger action
   - Ported XNA CnCNet Client MP save handling
+  - Retint fix toggle
 - **Uranusian (Thrifinesma)**:
   - Mind Control enhancement
   - Custom warhead splash list

docs/Whats-New.md

@@ -669,6 +669,7 @@ New:
 - Unit `Speed` setting now accepts floating point values (by Starkku)
 - `Strafing` is now disabled by default when using `Trajectory` (by CrimRecya)
 - Skip target scanning function calling for unarmed technos (by TaranDahl & solar-III)
+- Allow retint fix to be disabled with `[AudioVisual] -> UseRetintFix=no` in `rulesmd.ini` due to performance considerations (by Kerbiter)
 
 Vanilla fixes:
 - Allow AI to repair structures built from base nodes/trigger action 125/SW delivery in single player missions (by Trsdy)