Largely based on a_brief_introduction_to_our_source_repository_layout.html
from the website, revised and updated. I will delete the one from the
website and put a redirect to here once this is merged.
Change-Id: I06657bbea4c16df7bff1f2357cffd2ec8a63c65a
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7236
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
