Add push commands

[NRKirby]

I've added a section to gitalias.txt for push commands which I use frequently:

po

Useful for pushing to a branch, e.g:

$ git po dev

pom

Shortcut for pushing to the master branch, e.g:

$ git pom

[phdru]

Why? If you've configured origin as the upstream remote for the branches bare git push pushes the current branch to the upstream.

[erikmd]

@NRKirby as pointed out by @phdru it suffices to type git push, which is not that longer than git pom ;)
FYI this behavior of git push is explained in this other interesting repo; hoping this helps.

[joelparkerhenderson]

Close because git push handles this common case.