usage:
zipalign : you can find that tool in your Android/sdk/build-tools/23.0.3/ folder
-f : replaces existing file
-v : verbose output
4 : required by Android alignment bytes
input apk : already signed APK as it comes out from Android Studio
output APK : file you will upload to Google Play Developer Console
> 23.0.3 $ pwd
/Users/ukilucas/Library/Android/sdk/build-tools/23.0.3
> 23.0.3 $
> 23.0.3 $
./zipalign -f -v 4 ~/CyberFit-release-23.apk ~/CyberFit-release-23_aligned.apk