Write a tuning guide

[gabemontero]

We have a burgeoning list of tuning options for the controller, and some of those options have cause/effect relationships.

There are also potential tekton level tuning considerations we may want to touch upon or reference if they are cited in tekton doc.

@SaschaSchwarze0 @ImJasonH FYI ... please add any refs to other discussion threads, github or slack, if you have them.

But minimally, see https://github.com/shipwright-io/build/pull/649#issuecomment-793949110