rtpengine: document new T.38 options

src/modules/rtpengine/doc/rtpengine_admin.xml

@@ -2404,6 +2404,23 @@ rtpengine_offer();
 				and used for transcoding on the offering side.Useful only in combination with codec-transcode. <emphasis>all</emphasis> keyword
 				can be used to mask all offered codecs
 				</para></listitem>
+				<listitem><para>
+				<emphasis>T.38=decode</emphasis> - If the offered &sdp; contains a media section
+				advertising T.38 over UDPTL, translate it to a regular audio media section
+				over RTP. By default, PCMU and PCMA will be used as audio codecs, but that can
+				be overriden using the codec options described above. Other transport protocols
+				(e.g. SRTP) can also be selected in the same way. If the offered &sdp; does not
+				contain a T.38 section, then this flag has no effect.
+				</para></listitem>
+				<listitem><para>
+				<emphasis>T.38=force</emphasis> - Any audio media section (over RTP) in the
+				offered &sdp; will be translated into a T.38 section over UDPTL.
+				</para></listitem>
+				<listitem><para>
+				<emphasis>T.38=stop</emphasis> - Stops a previously established T.38 to audio
+				gateway and reverts the session back to media passthrough. This is useful when
+				handling a rejected T.38 offer.
+				</para></listitem>
 			</itemizedlist>
 			<para>
 			 Check also the documentation of RTPEngine, these flags are documented there as well: