doc: update precommit.md
doc: update precommit.md

This change removes internal information about Google workstations from documentation.

Change-Id: I9284ee56d6fe2364b36e4146a16bfca50e7fc90a
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/242779
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite