Add documentation

Readme.md

@@ -3,6 +3,30 @@
 
   Turn an Express-style path string such as `/user/:name` into a regular expression.
 
+## Usage
+
+```javascript
+var pathToRegexp = require('path-to-regexp');
+```
+### pathToRegexp(path, keys, options)
+
+ - **path** A string in the express format, an array of such strings, or a regular expression
+ - **keys** An array to be populated with the keys present in the url.  Once the function completes, this will be an array of strings.
+ - **options**
+   - **options.sensitive** Defaults to false, set this to true to make routes case sensitive
+   - **options.strict** Defaults to false, set this to true to make the trailing slash matter.
+
+```javascript
+var keys = [];
+var exp = pathToRegexp('/foo/:bar', keys);
+//keys = ['bar']
+//exp = /^\/foo\/(?:([^\/]+?))\/?$/i
+```
+
+## Live Demo
+
+You can see a live demo of this library in use at [express-route-tester](http://forbeslindesay.github.com/express-route-tester/).
+
 ## License
 
   MIT