Content: pricing page FAQ

[agjohnson]

We simplified the pricing page in #34 but might want to decide on where some of that existing content would fit. Some of this content should be in our docs, but there are some legitimate questions that might be good to cover on the pricing page.

This content came from https://readthedocs.com/pricing/ originally

• From https://github.com/readthedocs/site-community/pull/34/files/489fa1c3d035b03f672aef50d15cbd81a9db2771..3a673c9660e20d06360fd29765eedeeea4cd67a0#diff-491a1de3a551dd951ebc5ae1522e67760f145a1d805150610d7fcc58a441a81f