Added more text about adding test cases

README.md

@@ -201,6 +201,8 @@ Once installed the tests can be run from the project root using:
 
   mocha test/run.js
 
+New test cases can easily be added.  Create a markdown file (ending in `.md`) which contains the markdown to test.  Create a `.html` file of the exact same name.  It will automatically be tested when the tests are executed with `mocha`.
+
 
 Credits
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