Minor tweaks to README and ex_doc configuration

Summary:
* Set `README` as the documentation entry point
* Include `LICENSE` file in `ex_doc` documentation
* Add explicit copyright to `README`
* Add links to terms of use and privacy policy
* Remove link to Contributing section (contribution guidelines live in `.github` and are already rendered by GitHub
* Remove obsolete reference to release process

Reviewed By: alanz

Differential Revision: D85038135

fbshipit-source-id: e6126f8ac25effce189d2d0ec0f35a779fc423ad

Initial commit

fbshipit-source-id: 283a7db17e9c863b0c857d5464c35cfa12f4b930