json: some enhancements to the docs

- referring to jansson module for more complex json operations
- added id to exported function section

modules/json/README

@@ -47,7 +47,10 @@ Chapter 1. Admin Guide
 
 1. Overview
 
-   This module provides operations on json strings.
+   This is a simple module allowing to retrieve values from a JSON string.
+
+   For more complex operations with JSON documents, see the JANSSON
+   module.
 
 2. Dependencies
 

modules/json/doc/json_admin.xml

@@ -14,7 +14,12 @@
 	<section>
 	<title>Overview</title>
 	<para>
-		This module provides operations on json strings.
+		This is a simple module allowing to retrieve values from
+		a JSON string.
+	</para>
+	<para>
+		For more complex operations with JSON documents,
+		see the JANSSON module.
 	</para>
 	</section>
 
@@ -51,7 +56,7 @@
 
 	<section>
 	<title>Functions</title>
-	<section>
+	<section id="json.f.json_get_field">
 	    <title>
 		<function moreinfo="none">json_get_field(json_string, field_name, destination)</function>
 	    </title>