Currently it is only possible for the repo owner to set Email Notifications for pushes (About email notifications for pushes to your repository - GitHub Docs).
I realized that it would be a great feature if non-owners could also create such notifications for a repo. Currently I see no possibility to do that when I am working on an repo another person created.
Maybe it would be even great to enable Web notifications instead of Mail notifications.
Hope this helps improving github!
Till (pronoun me however you like)