Add CLI docs for tmuxp shell

Author: tony

tmuxp/cli.py

@@ -672,6 +672,14 @@ def startup(config_dir):
     help='Instead of opening shell, execute python code in libtmux and exit',
 )
 def command_shell(session_name, window_name, socket_name, socket_path, command):
+    """Launch python shell for tmux server, session, window and pane.
+
+    Priority given to loaded session/wndow/pane objects:
+    - session_name and window_name arguments
+    - current shell: environmental variable of TMUX_PANE (which gives us window and
+      session)
+    - ``server.attached_session``, ``session.attached_window``, ``window.attached_pane``
+    """
     server = Server(socket_name=socket_name, socket_path=socket_path)
 
     current_pane = None