Add usage information

Author: johno

README.md

@@ -11,9 +11,14 @@ npm install --save postcss-cssstats
 ## Usage
 
 ```javascript
-var postcssCssstats = require('postcss-cssstats');
-
-postcssCssstats();  // => true
+var postcss = require('postcss');
+var cssstats = require('postcss-cssstats');
+
+var output = postcss([
+  cssstats(function(stats) {
+    console.log(stats);
+  }))
+  .process(css);
 ```
 
 ## License

package.json

@@ -8,7 +8,8 @@
     "test": "test"
   },
   "scripts": {
-    "test": "jshint . && mocha test"
+    "test": "mocha test",
+    "hint": "jshint ."
   },
   "repository": {
     "type": "git",