Add CI

[magistau]

This PR adds CI that automatically runs README.sh on every commit. There's one disadvantage: the commit author has to update their commit history. You can do

git config pull.rebase true

Then git pull should be enough.

Alternative

Make CI just check if README.md matches the one generated by the script, then all contributors would have to run the script. Can be solved by using pre-commit hook. See j0hnmeow/awfice#1.