SSH key config check #128

GitHub:

❯ ssh -T git@github.com
Hi legowerewolf! You've successfully authenticated, but GitHub does not provide shell access.

GitLab:

❯ ssh -T git@gitlab.com
Welcome to GitLab, @legowerewolf!

Tangled:

❯ ssh -T git@tangled.sh
access denied: we don't serve interactive shells :)

It would be nice if Tangled could show a more personalized message to help you check that you're authenticating correctly.