topoh: added note about making call-id when dialog module is used

modules/topoh/README

@@ -147,6 +147,10 @@ modparam("topoh", "mask_ip", "192.168.0.1")
    encode Call-id in such cases. Well-known extensions such as call
    transfer or conference join will be added to work with encoded Call-id.
 
+   NOTE: if you are using dialog module to terminate calls and this
+   parameter is enabled, you must set the dialog module parameter
+   'lreq_callee_headers' to include the header: 'TH: dlh\r\n'.
+
    Default value is 0 (do not mask).
 
    Example 1.3. Set mask_callid parameter

modules/topoh/doc/topoh_admin.xml

@@ -117,6 +117,11 @@ modparam("topoh", "mask_ip", "192.168.0.1")
 			call transfer or conference join will be added to work with encoded
 			Call-id.
 		</para>
+		<para>
+			NOTE: if you are using dialog module to terminate calls and this
+			parameter is enabled, you must set the dialog module parameter
+			'lreq_callee_headers' to include the header: 'TH: dlh\r\n'.
+		</para>
 		<para>
 		<emphasis>
 			Default value is 0 (do not mask).