Update README.md

Author: operando

README.md

@@ -8,3 +8,4 @@ Android Code Reading History
 * [まったりAndroid Framework Code Reading #1 まとめ](https://github.com/AndroidFrameworkCodeReading/CodeReadingHistory/wiki/%E3%81%BE%E3%81%A3%E3%81%9F%E3%82%8AAndroid-Framework-Code-Reading-%231)
 * [まったりAndroid Framework Code Reading #2 まとめ](https://github.com/AndroidFrameworkCodeReading/CodeReadingHistory/wiki/%E3%81%BE%E3%81%A3%E3%81%9F%E3%82%8AAndroid-Framework-Code-Reading-%232)
 * [まったりAndroid Framework Code Reading #3 まとめ](https://github.com/AndroidFrameworkCodeReading/CodeReadingHistory/wiki/%E3%81%BE%E3%81%A3%E3%81%9F%E3%82%8AAndroid-Framework-Code-Reading-%233)
+* [まったりAndroid Framework Code Reading #4 まとめ](https://github.com/AndroidFrameworkCodeReading/CodeReadingHistory/wiki/%E3%81%BE%E3%81%A3%E3%81%9F%E3%82%8AAndroid-Framework-Code-Reading-%234)