New guide section on Git and GitHub

[Andrew Moore]

On Apr 14, 2018, at 4:01 PM, Jonathan Stickel <jjstickel at gmail.com> wrote:
> 
> Sure, it makes perfect sense to encourage PRs while continue to consider patches. I'm not against that at all, and I'm willing to figure it out. But care should be taken about the tone of the message, especially given the current competition. Any perception that Macports is not friendly to new users and contributors would be a mistake.

Jonathan,
I’ll take the blame for the tone.  This is not my first transgression, and I apologize both to you and the MacPorts folks.
-AM