JSON node: Add link to JSON schema spec in node help

nodes/core/parsers/70-JSON.html

@@ -58,6 +58,8 @@
        receives a String, no further checks will be made of the property. It will
        not check the String is valid JSON nor will it reformat it if the format option
        is selected.</p>
+    <p>For more details about JSON Schema you can consult the specification
+    <a href="http://json-schema.org/latest/json-schema-validation.html">here</a>.</p>
 </script>
 
 <script type="text/javascript">