Guide people with suggested pg config params

[begriffs]

Why are we implementing it? (sales eng)

What are the typical use cases?

When running Citus on prem people should adjust the default postgresql.conf parameters for better performance.

Communication goals (e.g. detailed howto vs orientation)

Good locations for content in docs structure

How does this work? (devs)

Example sql

Corner cases, gotchas

Are there relevant blog posts or outside documentation about the concept/feature?

Link to relevant commits and regression tests if applicable