Github maintenance

Initial documenation for how to maintain the infra on GitHub.

Follow these instructions:

[https://help.github.com/en/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent#adding-your-ssh-key-to-the-ssh-agent]

The paste the following into your .profile or equivalent file:

# Make sure that the ssh agent has touched git@github.com.
# Required for smooth operation of https://github.com/divvun/project-dadmin:
ssh -T git@github.com &>/dev/null