Provide more thorough defaults in the configuration guide template

Summary: Feedback from @makinde. These are easy (and necessary) to configure so
we might as well give the user a heads up.

Test Plan: Regenerated the documentation and read "Configuration Guide".

Reviewers: Makinde, jungejason, nh, tuomaspelkonen, aran

Reviewed By: Makinde

CC: aran, Makinde

Differential Revision: 929