Clean up example in README.

`-j` should usually not be necessary if the server is
correctly configured. So this is removed from the example
where it was used.

README.md

@@ -138,7 +138,7 @@ cat message.txt | ./go-sendxmpp -f ./sendxmpp recipient1@example.com recipient2@
 Send a message to two recipients directly defining account credentials.
 
 ```bash
-cat message.txt | ./go-sendxmpp -u bob@example.com -j example.com -p swordfish recipient1@example.com recipient2@example.com
+cat message.txt | ./go-sendxmpp -u bob@example.com -p swordfish recipient1@example.com recipient2@example.com
 ```
 
 Send a message to two groupchats (`-c`) using a configuration file.