add doc about literal caps in performance.rst

[zooko]

The description of the performance costs of immutables in docs/performance.rst​ neglects the "literal caps" optimization. Fix that, and close this ticket!

[daira]

I don't think the literal optimization changes any asymptotic costs, does it?

[zooko]

Replying to daira:

I don't think the literal optimization changes any asymptotic costs, does it?

I think of docs/performance.rst​ as supposed to tell you "What you need to know" about performance, not only the asymptotic costs. My attempt at answering that assumed that the asymptotic costs were often "What you need to know", but sometimes you need to know more.

Oh, and actually the literal optimization totally *does* change the asymptotic costs of some things. For example, the cost in network usage to upload N files of 200 bytes each is O(N) network usage. The cost to upload N files of 55 bytes each is zero network usage.

[marlowe]

Follow up with Brian on exact verbiage.