Update CHANGELOG.md

Author: jacksonrl

pkgs/ffigen/CHANGELOG.md

@@ -9,6 +9,8 @@
 - __Breaking change__: Certain synthetic USRs have been modified to ensure they
   cannot collide with real USRs. It's very unlikely that any user facing USRs
   are affected.
+- __Breaking change__: Dart const values will be generated for global variables marked const in C (e.g. static const int) instead of symbol lookups. This supports integers, doubles, and string literals. Including the variable name in the globals -> symbol-address configuration will still generate symbol lookups.
+
 
 ## 20.1.1