[functorch] Docs website modification (pytorch/functorch#563)
I modified the docs website:
- It has a new install page which we'll fill out l ater
- It has a new "whirlwind tour" section with is just our README
copy-pasted
- It has a "UX Limitations" section describing arbitrary python
mutation, in-place operations, and control flow.
Please let me know if you think anything else should be here.
Future work:
- I'm going to put up a table of what operators we have support for and
which ones we don't, autogenerated via OpInfo
