[extensions] Update security FAQ with note about "annoyance extensions"

Bug: N/A
Change-Id: Ief81d7e11dce27974eba862996715f92ed5b38d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4558671


Reviewed-by: David Bertoni <dbertoni@chromium.org>
Reviewed-by: Adrian Taylor <adetaylor@chromium.org>
Commit-Queue: Tim <tjudkins@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1149376}