Adding Readme (#8)

* Added readme

* Added an example how to run

Author: Nyholm

README.md

@@ -0,0 +1,7 @@
+# Code block checker
+
+Make sure that code blocks have valid syntax and can actually run.
+
+```terminal
+./code-block-checker.php verify:docs /path/to/docs cache.rst controller.rst --env=dev
+```