Add OWNERS for docs/

R=hablich@chromium.org, mathias@chromium.org

Bug: v8:9247
Change-Id: I3db662986dd36d4b29c6bd485b911ebf377e7533
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1613237Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61524}

docs/OWNERS

+hablich@chromium.org
+mathias@chromium.org