Added README text to include the info on including custom and pre-bui…

…lt schemas

README.md

@@ -9,6 +9,11 @@ of the [jQuery](http://jquery.com) library. When you view the page, a list
 will appear in the bottom left listing all the microdata objects detected
 on the page.
 
+In addition, you need to provide the schemas to validate against; some are already
+implemented in `schemas.js` which is to be included immediately after the
+`jquery.microdata.js` script. To add your own, you can use the
+`$.microdata.addDefinition(url, fields)` function as used in `schemas.js`.
+
 This tool is a work-in-progress and still doesn't adhere to the full specs (yet).
 Plans to support the full microdata spec + data vocabulary validation are on
 the drawing board. ;)