Mostly mentioning other platforms where older documentation mentioned
only Windows.

Bug: angleproject:1944
Change-Id: Ib020892fbdee22d3dc60aa71ac6b3c5f504728c4
Reviewed-on: https://chromium-review.googlesource.com/c/1430559Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>