Document Supported features (#67)

* Add initial docs for supported features

* Sections for JWK and JWE

* Document supported JWK features

* Document JWE support

* Change wording

README.md

@@ -3,6 +3,7 @@
 [![Build Status](https://travis-ci.org/lawliet89/biscuit.svg)](https://travis-ci.org/lawliet89/biscuit)
 [![Crates.io](https://img.shields.io/crates/v/biscuit.svg)](https://crates.io/crates/biscuit)
 [![Repository](https://img.shields.io/github/tag/lawliet89/biscuit.svg)](https://github.com/lawliet89/biscuit)
+[![Documentation](https://docs.rs/biscuit/badge.svg)](https://docs.rs/biscuit)
 
 - Documentation:  [stable](https://docs.rs/biscuit/) | [master branch](https://lawliet89.github.io/biscuit)
 - Changelog: [Link](https://github.com/lawliet89/biscuit/blob/master/CHANGELOG.md)
@@ -23,3 +24,10 @@ To use the latest `master` branch, for example:
 ```toml
 biscuit = { git = "https://github.com/lawliet89/biscuit", branch = "master" }
 ```
+
+## Supported Features
+
+The crate, does not support all, and probably will never support all of
+the features described in the various RFCs, including some algorithms and verification.
+
+See the [documentation](https://github.com/lawliet89/biscuit/blob/master/doc/supported.md) for more information.

doc/README.md

@@ -0,0 +1,6 @@
+# Documentation
+
+For API documentation, refer to the links below. This directory serves auxiliary documentation that are linked from
+the API documentation.
+
+[stable](https://docs.rs/biscuit/) | [master branch](https://lawliet89.github.io/biscuit)