Document usage with a toolbox container for immutable distros

[VarLad]

I think its worth it to document this as an alternate way to run opengamepadui for immutable distros. I run opengamepadui with gamescope -w 1920 -h 1080 -f --xwayland-count 2 -- toolbox run -c name-of-the-container dbus-run-session -- /usr/share/opengamepadui/opengamepad-ui.x86_64 -f
gamescope itself is widely packaged in many distros, so it can be easily installed inside the host.

[ShadowApex]

The repository for documentation is located here:
https://github.com/ShadowBlip/OpenGamepadUI-docs

I do not have experience with toolbox to add this, but we welcome contributions if you wanted to add steps for this.