db_mongodb: added Remarks section to collect details about specific requirements

src/modules/db_mongodb/doc/db_mongodb_admin.xml

@@ -10,9 +10,9 @@
 <!-- Module User's Guide -->
 
 <chapter>
-	
+
 	<title>&adminguide;</title>
-	
+
 	<section>
 	<title>Overview</title>
 	<para>
@@ -30,7 +30,7 @@
 	</para>
 	</section>
 
-	<section>
+	<section id="db_mongodb.s.limitations">
 	<title>Limitations</title>
 	<para>
 		This module has implemented the equivalent operations for INSERT,
@@ -42,6 +42,17 @@
 	</para>
 	</section>
 
+	<section id="db_mongodb.s.remarks">
+	<title>Remarks</title>
+	<para>
+		Using this module as a database dirver may require additional settings
+		for various modules. For example, you have to set module parameter
+		'db_insert_null' to 1 for 'usrloc' module. If the module you are using
+		with 'db_mongodb' fails, check its README for notes about using it
+		with no-SQL databases.
+	</para>
+	</section>
+
 	<section>
 	<title>Dependencies</title>
 	<section>