Rest-API to Signal-CLI Home Assistant add-on
Install the add-on, choose your desired port, start.
After the add-on is started follow the directions at the link below starting from "Register phone number"
https://github.com/bbernhard/signal-cli-rest-api/blob/master/doc/HOMEASSISTANT.md
Then proceed here:
https://www.home-assistant.io/integrations/signal_messenger/
If you want to use i.e. REST to receive messages in HA, you can find more details here
All credit to @bbernhard, all I did was take their work and make an add-on.