Create a Performance guide

[wwwillchen]

@richard-to I think we need some kind of guide. Technically all the information is in https://google.github.io/mesop/api/config/ but it's not obvious to look there. I think having some kind of "Performance" guide would be very helpful.

Something like:

• How do I diagnose my performance problem? e.g. is it because state is too large or some other reason
• If state is a problem, how do I pick which state session backend is suitable?

[richard-to]

Yeah, I agree. I think it would definitely be helpful. Definitely the info in config is a bit messy and unorganized. I think the main thing is to be able to distill the information in a way that is clear and concise.

And in terms of the state session backends, I do feel that we need to do some more loading testing on the various options to see how they actually fare.