Warn if `origin/gh-pages` exists and the local `gh-pages` branch is not synced to it

[kevmoo]

[kevmoo]

This will be some combination of git config --list to see if the current branch or "master" is tracking a remote (likely origin)

If yes, then use git show-ref to see if refs/remotes/origin/TARGET_BRARCH exists (likely gh-pages)

If so, then see if a local gh-pages exists, if not – yell about wiring up the remote...right?