Add command for members to invite themselves to our GitHub Org

[with-heart]

We currently have a manual process in place for members to be invited to our GitHub Org.

I'd like to automate this by adding a command to the bot, perhaps /github-invite <github-username> or something along those lines.

We'd need to research how to authenticate that the user is who they say they are so that members can't invite just anyone to the org.