Add tooltip for `cmd/ctrl-enter` to commit. Remove `tab` to focus button
Add tooltip for `cmd/ctrl-enter` to commit. Remove `tab` to focus button

Previously, hitting tab to select a co-author would also focus the
commit buttin, which is not desired.

Co-Authored-By: Matt <f9042c580f8225752e6ba54a413801a3d33eefad@users.noreply.github.com>

atom/github,atom/github,atom/github