rr: docs - note about format of record_route_preset() parameters

(cherry picked from commit f318fab)

src/modules/rr/doc/rr_admin.xml

@@ -507,8 +507,8 @@ remove_record_route();
       <title><function moreinfo="none">record_route_preset(string
       [,string2])</function></title>
 
-      <para>This function will put the string into Record-Route, don't use
-      unless you know what you are doing.</para>
+      <para>This function will put the string params into Record-Route, avoid
+      to use it unless you know what you are doing.</para>
 
       <para>Meaning of the parameters is as follows:</para>
 
@@ -528,6 +528,13 @@ remove_record_route();
       to the outbound interface and the 'string2' param is pointing to the
       inbound interface.</para>
 
+      <para>Note: The value of parameters must not contain the SIP protocol
+	  scheme (sip: or sips:), one is added based on routing requirements. Thus
+	  the value has to be like "address:port;parameters", the port and
+	  parameters are optional. If the second parameter is provided, do not
+	  forget to add the parameter "r2=0" so the proxy processes both
+	  corresponding Route headers at once.
+
       <para>When the <quote>outbound</quote> module was loaded before this
       module this function will determine whether outbound is required for the
       request and generate and add a flow-token as the username part of the