Added docs for systemd usage.

Author: peteches

docs/automatic_start.md

@@ -24,3 +24,12 @@ Config options:
 ### Linux
 
 Help with this would be greatly appreciated. Please get in touch.
+
+#### Systemd
+
+##### this will only start the tmux server, it will *not* start any terminal emulator
+
+To enable automatic start with systemd:
+- Put `set -g @continuum-boot 'on'` in tmux.conf
+- reload tmux config with this shell command: `$ tmux source-file ~/.tmux.conf`
+- see [systemd](./systemd_details.md) for more details about how this is implemented

docs/systemd_details.md

@@ -0,0 +1,7 @@
+# Systemd autmatic start for tmux
+
+The first time tmux starts when '@continuum-boot' is set to 'on' tmux-continuum will generate a user level systemd unit file which it will save to `${HOME}/.config/systemd/user/tmux.service` and enable it. From then on when that user logs in, either through a gui session or on the console or via ssh, Systemd will start the tmux server.
+
+The command used to start the tmux server is determined via the '@systemd_tmux_server_start_cmd' option that can be set in .tmux.conf. (Remeber to reload your configuration with `tmux source ~/.tmux.conf` afterwards.
+
+The default command to use is `new-session`. If you want more control over what sessions get started then you should set up your sessions in tmux.conf and set @systemd_tmux_server_start_cmd to 'start-server'