Add testing info to readme

Author: Simon Yousoufov

README.md

@@ -12,6 +12,12 @@ use Fuzz\HttpException\AccessDeniedHttpException;
 throw new AccessDeniedHttpException('Access denied.');
 ```
 
+## Testing
+`phpunit`
+
+## Code Coverage
+`phpunit --coverage-html tests/coverage && open tests/coverage/index.html`
+
 ## TODO
 1. Support all HTTP status codes
 1. Improve exception API