Added note on keystore and password format

docs/en/manuals/android.md

@@ -46,7 +46,7 @@ If you want the editor to automatically create random debug certificates, leave
 
 ![Signing Android bundle](images/android/sign_bundle.png)
 
-If you want to sign your bundle with a particular keystore, specify the *Keystore* and *Keystore password* files:
+If you want to sign your bundle with a particular keystore, specify the *Keystore* and *Keystore password*. The *Kyestore* is expected to have the `.keystore` file extension while the password is expected to be stored in a text file with the `.txt` extension:
 
 ![Signing Android bundle](images/android/sign_bundle2.png)