Add EXPORT_KEEPALIVE to ChangeLog.md

Author: DavidPeicho

ChangeLog.md

@@ -21,6 +21,10 @@ See docs/process.md for more on how version tagging works.
 3.1.33 (in development)
 -----------------------
 - Update SDL2_ttf port to 2.20.2 (#18804)
+- Added `-sEXPORT_KEEPALIVE` to export symbols. When using
+  `MINIMAL_RUNTIME`, the option will be **disabled** by default.
+  This option simply exports the symbols on the module object, i.e.,
+  `Module['X'] = X;`
 
 3.1.32 - 02/17/23
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