db_mongodb: updated details in docs about the limitations

(cherry picked from commit 6940ce0e991fd5b6af9ef5822dc2b1a324319174)

modules/db_mongodb/doc/db_mongodb_admin.xml

@@ -34,8 +34,12 @@
 	<itemizedlist>
 	<listitem>
 	<para>
-		This module has implemented INSERT, UPDATE and DELETE. Query
-		(SELECT) is not yet storing the result.
+		This module has implemented the equivalent operations for INSERT,
+		UPDATE, DELETE and SELECT. The match condition (WHERE clause)
+		works with the operators: equal, not equal, greater than, less than,
+		equal or greater than, equal or less than. Raw query is not
+		implemented inside this module, use ndb_mongodb for sending any
+		kind of command to a MongoDB server.
 	</para>
 	</listitem>
 	</itemizedlist>