R1:8391767d8ca2

Improve setup process / documentation for outbound email configuration

Summary:
ccheever did an install and gave me some feedback about issues he hit. This
tries to:

- properly document how to configure outbound email;
- test outbound email configuration in the setup mode;
- provide basic daemon documentation;
- document that phabricator.base-uri is required for all installs.

Test Plan:
read documentation, jumped through all the setup branches to test configuration
error detection

Reviewed By…