River is a dynamic tiling Wayland compositor with flexible runtime
configuration based on wlroots.
River can either be run nested in an X11/Wayland session or 
directly from a tty using KMS/DRM. Simply run the river command.

On startup river will run an executable file at
$XDG_CONFIG_HOME/river/init if such an executable exists. 
If $XDG_CONFIG_HOME is not set, ~/.config/river/init will 
be used instead.
Usually this executable is a shell script invoking riverctl(1) 
to create mappings, start programs such as a layout generator
or status bar, and perform other configuration.
For complete documentation see the river(1), riverctl(1), and 
rivertile(1) man pages
here is an example of init to river
it goes in /home/youruser/.config/river 
https://github.com/riverwm/river/blob/master/example/init
edit it as you like.