Document use of tmux

Author: mpilgrem

doc/maintainers/self-hosted_runners.md

@@ -26,6 +26,26 @@ Occasionally Oracle will turn off the machine because:
 With the appropriate authority installed on the server, the runner can be
 managed remotely using SSH, with command `ssh [email protected]`.
 
+This is best done using [`tmux`](https://github.com/tmux/tmux/wiki), a terminal
+multiplexer, as follows:
+~~~sh
+$ # In a shell, command tmux to create a new session with a single window with a
+$ # single pane (a pseudo terminal). The session will be displayed on the screen
+$ # by a client:
+$ tmux new-session
+$ # Send the following command to that pseudo terminal, to connect to the
+$ # remote host:
+$ ssh [email protected]
+$ # In the remote host, change to the actions-runner directory:
+$ cd actions-runner
+$ # In the remote host, start the runner:
+$ ./run.sh
+$ # Detach the current client from the session by the key combination of
+$ # 'C-b' 'd' (where 'C-b' is CTRL+b). The session will continue to run in the
+$ # background:
+$ C-b d
+~~~
+
 The available disk space can be queried with command `df -h`; the relevant entry
 is for filesystem `/dev/sda1`.