Lefthook support

[Falco]

I used it for the first time today, and it’s great that I had to do zero setup in my machine for it.

Thanks for the pull request!

@pfaffman

Can you say more about what Lefthook is and why we’d want to know more about it? Maybe a link to it and a use case?

There is context here:

https://github.com/discourse/discourse/pull/7826