Add documentation about troubleshooting HTTPS problems

Summary:
I got to learn a lot about SSL/TLS today.

Try to make it easier to troubleshoot SSL issues.

Test Plan: Read document.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2132

Differential Revision: https://secure.phabricator.com/D4079