Instructions how to setup watchman

[stepancheg]

I'm using sl over git repo.

Whatever I tried, I could not make sl talk to watchman (operations are slow, and no mention of sl requests in watchman logs).

Is sapling meant to work with watchman? Watchman is mentioned briefly in the documentation in context of ISL, so it is not clear.

Maybe provide a documentation:

• how to setup watchman
• how to verify watchman is used