Update README.md

Author: mlynch

README.md

@@ -1,3 +1,5 @@
 ### :point_right: Deprecated! Please use [`cordova-plugin-ionic-keyboard`](https://github.com/ionic-team/cordova-plugin-ionic-keyboard) :point_left:
 
+See this comment for API changes needed to move to new plugin: https://github.com/ionic-team/ionic-plugin-keyboard/issues/305#issuecomment-364198332
+
 * Installation, API docs: [README_OLD.md](https://github.com/ionic-team/ionic-plugin-keyboard/blob/master/README_OLD.md)