chore: Add README to release please & change version strategy

#non-breaking

PiperOrigin-RevId: 782918726

Author: Poggecci

.github/release-please.yml

@@ -1,5 +1,6 @@
 releaseType: maven
 handleGHRelease: true
-bumpMinorPreMajor: false
+bumpMinorPreMajor: true
 extraFiles:
-  - core/src/main/java/com/google/adk/Version.java
+  - core/src/main/java/com/google/adk/Version.java
+  - README.md