Fix documentation error.
Fix documentation error.

Summary:
This little error is causing the table of contents to be messed up.
See: https://facebook.github.io/watchman/docs/install.html
It has two entries on left side for 'watchman-wait' and is missing
an entry.

Reviewed By: wez

Differential Revision: D5835138

fbshipit-source-id: ea82e16fb12c55a03dc7e4a49c045e33587f6956

wez/watchman,wez/watchman,nodakai/watchman,kwlzn/watchman,nodakai/watchman,wez/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,kwlzn/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,wez/watchman,facebook/watchman,kwlzn/watchman,kwlzn/watchman,wez/watchman,kwlzn/watchman,wez/watchman,kwlzn/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,wez/watchman,facebook/watchman,wez/watchman,facebook/watchman,kwlzn/watchman,nodakai/watchman