[autotest] Link to rpc docs in comments in frontend.py

Docs are nice. It's a shame to link to nonexistant ones, and not link to
existant ones.

BUG=NONE
TEST=NONE

Change-Id: I5c20053926b9cb22e7314cedb27ae73f9906ccfe
Reviewed-on: https://gerrit.chromium.org/gerrit/50351
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Commit-Queue: Aviv Keshet <akeshet@chromium.org>
1 file changed