Update HOMEASSISTANT.md

Adding a description on how signal-cli-rest-api can trigger automations in Home Assistant. (Sending messages to Signal to trigger events)

doc/HOMEASSISTANT.md

@@ -6,7 +6,7 @@ This document covers the following topics:
 * [Installation](#installation)
 * [Set up a phone number](#set-up-a-phone-number)
 * [Sending messages to Signal Messenger groups](#sending-messages-to-signal-messenger-groups)
-
+* [Sending messages to Signal to trigger events](##sending-messages-to-signal-to-trigger-events)
 See also the [documentation of the Home Assistant integration](https://www.home-assistant.io/integrations/signal_messenger/).
 
 ## Installation
@@ -174,6 +174,33 @@ In order for groups to show up in the `groups` list, try the following steps:
   curl -X GET -H "Content-Type: application/json" 'http://127.0.0.1:8080/v1/receive/<number>'
   ```
 
+## Sending messages to Signal to trigger events
+In this example, we will be using signal-cli-rest-api to as a Home Assistant trigger. For example, you would be able to write 'light' to your Signal account linked to signal-cli-rest-api and have Home Assistant adjust the lights for you. To accomplish this, you will need to edit the `rest.yaml` configuration of Home Assistant, add the following resource:
+```- resource: "http://127.0.0.1:8080/v1/receive/<number>"
+  headers:
+    Content-Type: application/json
+  sensor:
+    - name: "Signal message received"
+      value_template: '{{ value_json[0].envelope.dataMessage.message }}'
+  ```
+And then you can create an automation as follows:
+```alias: "[signal] message received"
+trigger:
+  - platform: state
+    entity_id:
+      - sensor.signal_message_received
+condition: []
+action:
+  - if:
+      - condition: state
+        entity_id: sensor.signal_message_received
+        state: <word to use for trigger>
+    then:
+      - service: <service to run>
+        data: {}
+mode: single
+```
+
 
 ## API details