servod: update README & FAQ for servodutil/watchdog

This adds a section each for servodutil and the servod watchdog to the
README files.

BUG=chromium:841121
TEST=visual inspection in gitiles

Change-Id: I53b7607e2baadd7c10fdca917c68824a9e3d9fd9
Signed-off-by: Ruben Rodriguez Buchillon <coconutruben@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1215105
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Mengqi Guo <mqg@chromium.org>
2 files changed