Can you please update the documenattion for ubuntu installation

[KarthikSamyak]

The below documentation says that we get .deb file from the latest releases but no release has the debian file created in the assets

https://facebook.github.io/watchman/docs/install#ubuntu-prebuilt-debs

[awilkins]

Suspect this is because of #1276

Hypothesis here would be that because installing all the libs that the Watchman build draws in breaks debtools, it cannot complete a Debian package as part of the build.

[RupanPrasai]

Here's a decent fix I found, but the version of watchman is not the current release with this method.

#1175 (comment)