Updated README with description and installation instructions.

README.MD

@@ -2,4 +2,33 @@
 
 [![Build Status](https://travis-ci.org/sagotch/ISO8601.ml.svg?branch=test)](https://travis-ci.org/sagotch/ISO8601.ml)
 
-ISO8601 date parsing for OCaml.
+ISO 8601 and RFC 3999 date parsing for OCaml.
+
+**Work in progress**
+
+## Permissive module
+
+Date, time, and datetime parsing function of this module are
+much more permissive than ISO 8601 or RFC 3339 specifications.
+
+Either basic and/or extended formats can be used for date and time,
+and no consistency is required (it is possible to mix basic format for
+date and extended format for time), lowercase letters can be used,
+and datetime separator may be a space character.
+
+Note: for now, this module is the only one available.
+
+## Installation
+
+Via opam:
+
+    opam install ISO8601
+
+From sources:
+
+    make build
+    make install
+
+## License
+
+Distributed under the terms of [MIT license](LISENCE).