Add note about contributor documentation to buildSrc

Author: daymxn

buildSrc/README.md

@@ -1,5 +1,8 @@
 ## Build Source
 
+> [!NOTE]
+> Eventually, this will be merged with our [contributor documentation](https://firebase.github.io/firebase-android-sdk/).
+
 This file will be more organized as time progresses. Because a lot of our
 plugins and systems require a moderate amount of cognitive overhead to understand,
 I thought it best to provide documentation for such systems. You can find the