Fix docs on missing module dependency.

If replicate_contacts_to parameter is turned on, usrloc depends on the clusterer module.
Credits go to Sammy on mailing list.

modules/usrloc/README

@@ -235,7 +235,9 @@ Chapter 1. Admin Guide
 1.2.1. OpenSIPS Modules
 
    The following modules must be loaded before this module:
-     * Optionally a database module.
+     * Optionally an SQL database module.
+     * clusterer, if replicate_contacts_to parameters is turned on
+       (contact replication via clusterer module).
 
 1.2.2. External Libraries or Applications
 

modules/usrloc/doc/usrloc_admin.xml

@@ -131,7 +131,14 @@
 			<itemizedlist>
 			<listitem>
 			<para>
-				<emphasis>Optionally a database module</emphasis>.
+				<emphasis>Optionally an SQL database module</emphasis>.
+			</para>
+			</listitem>
+			<listitem>
+			<para>
+				<emphasis>clusterer, if <xref linkend="replicate_contacts_to"/>
+				parameters is turned on (contact replication via clusterer 
+				module)</emphasis>.
 			</para>
 			</listitem>
 			</itemizedlist>