Added some references

Author: dantleech

documentation/index.md

@@ -9,7 +9,11 @@ title: Documentation
 
 ## Reference
 
-- [API Reference](/doc/html/index.html)
+- [API Reference](/doc/html/index.html) - Online API documentation for the PHPCR project.
+- [Node Type CND Reference (Jackrabbit)](http://jackrabbit.apache.org/node-type-notation.html) - Detailed definition and
+  explanation of the CND node type format.
+- [JCR Query Cheatsheet (Magnolia)](https://wiki.magnolia-cms.com/display/WIKI/JCR+Query+Cheat+Sheet) - Examples of
+  the JCR2 query language.
 
 ## Slides