adding phone alert documentation

admin_doc/source/phone_alerts.rst

+================================
+Phone alerts with Twilio
+================================
+
+Overview
+
+Setup through Twilio
+====================
+Get added as a developer to the LSC Twilio account (talk to Peter Shawhan or Leo Singer)
+Create a Twilio account (if needed)
+Go to Twilio Console.
+Copy Account SID to settings_secret.py
+Copy Auth token to settings_secret.py
+Same for URLs
+
+URLs `here <https://www.twilio.com/console/dev-tools/twiml-bins>`__.
+Console -> ellipsis -> developer center -> twiml bins
+
+Add documentation from Peter.
+
+Setup on GraceDB server
+=======================
+Discussion of how it's set up on the server.
+Mention how keys are in settings/settings_secret.py (not part of git repo)
+NOTE: settings_secret is