rtpengine: documented the flag for call recording

- reported by GH #1221

src/modules/rtpengine/doc/rtpengine_admin.xml

@@ -2036,7 +2036,7 @@ rtpengine_offer();
 				<listitem><para>
 				<emphasis>no-redis-update</emphasis> - this flag can be used by Kamailio in order
 				to tell rtpengine not to persist the call into Redis upon receiving offer/answer()
-				control commands. If flag is not set, default action is rtpengine persists call 
+				control commands. If flag is not set, default action is rtpengine persists call
 				to redis.
 				</para></listitem>
 				<listitem><para>
@@ -2273,7 +2273,16 @@ rtpengine_offer();
 				in the Sipwise rtpengine proxy. This is especially useful when the first call leg is handled
 				by some rtpengine machine while the second call leg is handled by other rtpengine machine.
 				</para></listitem>
+				<listitem><para>
+				<emphasis>record-call=on</emphasis> - instructs RTPEngine to record the session. Use
+				it in rtpengine_offer() to start recording immediately and save the call metadata,
+				as alternative to start_recording().
+				</para></listitem>
 			</itemizedlist>
+			<para>
+			 Check also the documentation of RTPEngine, these flags are documented there as well:
+			<ulink url="https://github.com/sipwise/rtpengine">https://github.com/sipwise/rtpengine</ulink>.
+			</para>
 		</listitem>
 		</itemizedlist>
 		<para>
@@ -2466,8 +2475,11 @@ rtpengine_manage();
 		<function moreinfo="none">start_recording()</function>
 		</title>
 		<para>
-		This function will send a signal to the &rtp; proxy to record
-		the &rtp; stream on the &rtp; proxy.
+		This function will send a signal to the &rtp; relay to record
+		the &rtp; stream flowing through it. See also the option
+		<quote>record-call=on</quote> for rtpengine_manage()/rtpengine_offer(),
+		which offers an alternative for call recording, saving also call
+		metadata from SDP.
 		</para>
 		<para>
 		This function can be used from REQUEST_ROUTE and ONREPLY_ROUTE.