Put this in .git/hooks/post-checkout, make it executable with chmod u+x .git/hooks/post-checkout. Now git will complain when you have to do pod install after witching branches. You can also symlink it to .git/hooks/post-merge so it also is run after merge/pull

post-checkout

#!/bin/bash
#
# Let's you know when your pods should be updated right after a git pull or git merge
# Also works for fast-forward pulls.
#
# To enable this hook for your project, save it as .git/hooks/post-checkout
 
diff "Podfile.lock" "Pods/Manifest.lock" > /dev/null
 
if [ $? != 0 ] ; then
    echo
    echo "[COCOAPODS] The sandbox is not in sync with the Podfile.lock."
    echo "            Run 'pod install' or update your CocoaPods installation."
    echo
    #pod install # uncomment this line to update the pods whenever necessary
fi