document -naccept option

doc/apps/s_server.pod

@@ -9,6 +9,7 @@ s_server - SSL/TLS server program
 
 B<openssl> B<s_server>
 [B<-accept port>]
+[B<-naccept count>]
 [B<-context id>]
 [B<-verify depth>]
 [B<-Verify depth>]
@@ -68,6 +69,10 @@ for connections on a given port using SSL/TLS.
 
 the TCP port to listen on for connections. If not specified 4433 is used.
 
+=item B<-naccept count>
+
+The server will exit after receiving B<number> connections, default unlimited. 
+
 =item B<-context id>
 
 sets the SSL context id. It can be given any string value. If this option