Supersize: Add FAQ

I wrote a FAQ for the UI with some help information, such as a table of
the keyboard shortcuts.

Demo:
https://notwoods.github.io/chrome-supersize-reports/FAQ

Bug: 847599
Change-Id: Ie1b132798750f07d23044c416f27196a773d38f6
Reviewed-on: https://chromium-review.googlesource.com/1142529
Commit-Queue: Tiger Oakes <tigero@google.com>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576578}
4 files changed