Update on release APK signing procedure

Building-AntennaPod.md

@@ -88,13 +88,16 @@ More commands can be found in the [Gradle Plugin User Guide](http://tools.androi
 
 ### Building a release APK with gradle
 
-- If you want the release APK to be signed by gradle automatically, you have to create a file called `gradle.properties` in the root of the project's directory.
+- If you want the release APK to be signed by gradle automatically, you have to create a file called `gradle.properties` in `app` sub-directory.
 - Add the following lines to the `gradle.properties` and replace the value to the right of the `=` with information about your keystore:
 
 		releaseStoreFile=keystore
 		releaseStorePassword=password
 		releaseKeyAlias=alias
 		releaseKeyPassword=password
+- Tips on [generating keystore](http://stackoverflow.com/questions/3997748/how-can-i-create-a-keystore)	
+- Note: the release APK you created **CANNOT** install over the APK from official distribution. Android's security 
+	check forbids so (your APK has a signature generated above, different from the one signed in the official one).
 
 #### Useful commands for building release versions with gradle