add info to kivy Readme

gui/kivy/Readme.txt

@@ -3,3 +3,9 @@ Commands::
     `make theming` to make a atlas out of a list of pngs
 
     `make apk` to make a apk
+
+
+If something in included modules like kivy or any other module changes
+then you need to rebuild the distribution. To do so:
+
+   `rm -rf electrum/.buildozer/android/platform/python-for-android/dist`