Add config section to controller docs

Addresses https://github.com/balderdashy/sails/issues/1425.

I'm not totally sure if this is the optimal place for this--not totally positive if every file pertains to 0.10.x or if some are 0.9.x--so if there's another obvious place to put this and it's worthwhile, let me know and I'll move it.

I think every documentation file--especially those with an overridable config (e.g. models)--could benefit a similar configuration subheading. That's a change I could make across more files, what do you think?