Add breaking.md

Author: Matei Nenciu

BREAKING.md

@@ -0,0 +1,15 @@
+## Versions
+
+- [Version 4.x.x](#version-4xx)
+
+## Version 4.x.x
+
+### Capacitor 4
+
+This plugin now supports Capacitor 4 only. Please run `npx cap sync` after updating this package.
+
+If you want to use this plugin with Capacitor 3, please install version `1.3.0`:
+
+```
+npm i @capacitor-firebase/crashlytics@1.3.0
+```