This is in preparation for adding more docs and migrating internal ones.

Bug: angleproject:1944
Change-Id: I7aa4d708c9cd6134ef4ded00a82890448988ce9e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1773907Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>