Add ssh client config recommendation

documentation/ssh.markdown

@@ -19,6 +19,30 @@ In case of a restrictive firewall, for instance in an hotel, you can also connec
 
 Linux and macOS workstations have SSH installed in all current default installations. For Windows we suggest [Putty SSH](http://www.putty.org/) as an SSH client.
 
+Configuration
+-------------
+
+We recommend the following client settings in your `~/.ssh/config`:
+
+```
+HashKnownHosts no
+ForwardAgent yes
+ForwardX11 yes
+
+ControlPersist 60s
+ControlMaster auto
+ControlPath ~/.ssh/ssh-%h-%p-%r
+```
+
+The last 3 variables enable the sharing of multiple sessions over a single network connection,
+which will speed up subsequent connections to the same host (i.e.: makes tab completion usable for ssh/scp commands).
+See also `man 5 ssh_config`.
+
+To override this and start a new session in a new connection:
+
+```bash
+ssh -o ControlMaster=no -o ControlPath=none user@host
+```
 
 Debugging tips
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