Update the "Connected Commands" section of s_client/s_server docs

Fixes #6307
Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/6330)

doc/man1/s_client.pod

@@ -667,10 +667,35 @@ on port 4433.
 
 If a connection is established with an SSL server then any data received
 from the server is displayed and any key presses will be sent to the
-server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
-have been given), the session will be renegotiated if the line begins with an
-B<R>, and if the line begins with a B<Q> or if end of file is reached, the
-connection will be closed down.
+server. If end of file is reached then the connection will be closed down. When
+used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
+given), then certain commands are also recognized which perform special
+operations. These commands are a letter which must appear at the start of a
+line. They are listed below.
+
+=over 4
+
+=item B<Q>
+
+End the current SSL connection and exit.
+
+=item B<R>
+
+Renegotiate the SSL session (TLSv1.2 and below only).
+
+=item B<B>
+
+Send a heartbeat message to the server (DTLS only)
+
+=item B<k>
+
+Send a key update message to the server (TLSv1.3 only)
+
+=item B<K>
+
+Send a key update message to the server and request one back (TLSv1.3 only)
+
+=back
 
 =head1 NOTES
 

doc/man1/s_server.pod

@@ -673,8 +673,9 @@ If a connection request is established with an SSL client and neither the
 B<-www> nor the B<-WWW> option has been used then normally any data received
 from the client is displayed and any key presses will be sent to the client.
 
-Certain single letter commands are also recognized which perform special
-operations: these are listed below.
+Certain commands are also recognized which perform special operations. These
+commands are a letter which must appear at the start of a line. They are listed
+below.
 
 =over 4
 
@@ -688,11 +689,12 @@ End the current SSL connection and exit.
 
 =item B<r>
 
-Renegotiate the SSL session.
+Renegotiate the SSL session (TLSv1.2 and below only).
 
 =item B<R>
 
-Renegotiate the SSL session and request a client certificate.
+Renegotiate the SSL session and request a client certificate (TLSv1.2 and below
+only).
 
 =item B<P>
 
@@ -703,6 +705,22 @@ cause the client to disconnect due to a protocol violation.
 
 Print out some session cache status information.
 
+=item B<B>
+
+Send a heartbeat message to the client (DTLS only)
+
+=item B<k>
+
+Send a key update message to the client (TLSv1.3 only)
+
+=item B<K>
+
+Send a key update message to the client and request one back (TLSv1.3 only)
+
+=item B<c>
+
+Send a certificate request to the client (TLSv1.3 only)
+
 =back
 
 =head1 NOTES