Text message from relay

Sooo,
I have this water level sensor. The relay turns on the pump when level to low, and turns off when level is max. Simple. Now. How to automatize it to get a text message each time it turns on and off?? I think it’s very simple, but cannot put my finger on it.
Please help.

You should look here: https://companion.home-assistant.io/en/notifications/basic