Add how to share a tmux session between users

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

share_tmux_session.md

@@ -0,0 +1,28 @@
+# How to share a tmux session accross users?
+
+It can be handy to share a tmux session between different user accounts, for
+example to allow a someone to look over your shoulder while you work on
+something.
+
+To do this, we need to have a folder with group permission shared between the
+two persons.
+
+In the Fedora infrastructure we can easily use the ``fi-apprentice`` group for
+this.
+
+So we have created the folder:
+
+* /var/tmux/shared  which is writable to the fi-apprentice group
+
+
+You can then create a tmux session using:
+
+::
+
+  tmux -S /var/tmux/shared new -s <name>
+
+And the other person(s) can join it using:
+
+::
+
+  tmux -S /var/tmux/shared att -t <name>