Correct Aphlict documentation for Nginx proxying

Summary: Fixes T10857. This documentation did not accurately reflect proper configuration: in the Aphlict config, SSL is inferred from the presence of ssl.* configuration.

Test Plan: Read documentation.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10857

Differential Revision: https://secure.phabricator.com/D15787