debug overwrite documentation

Add information about the debug overwrite behavior of .testing() to the documentation.

README.md

@@ -29,7 +29,8 @@ npm install --save letsencrypt-express
 ```javascript
 'use strict';
 
-// Note: using staging server url, remove .testing() for production
+/* Note: using staging server url, remove .testing() for production
+Using .testing() will overwrite the debug flag with true */ 
 var LEX = require('letsencrypt-express').testing();
 
 var lex = LEX.create({