Update docs

[GregoryConrad]

A lot of things have changed since the current version of the docs were written:

• [x] transactions
• [ ] #9
• [ ] Port over effect documentation/improve inline code docs
  • [x] like invalidating and refreshing futures
  • [x] Hydrate, replay

and we likely need to better document the following:

• [x] RearchBuilder
• [x] current builtin side effects
• [x] #8
• [x] #10
• [ ] #11
  • [ ] Capsules
  • [ ] Side effects
• [x] fpdart interop FAQ per https://github.com/GregoryConrad/rearch-dart/issues/79
• [ ] #12
  • Idea spun off of https://github.com/GregoryConrad/rearch-dart/issues/71

[GregoryConrad]

I want to get some of the improvements I made out, so spinning off the remaining TODOs in future issues so that what is done already can be shipped.