Update README to add an example of a published message in JSON format 📝

README.md

@@ -35,3 +35,13 @@ Or you can add a new entry in the `crontab`, like:
 ```sh
 */20 * * * * /usr/bin/python3 ~/scripts/mijia-temperature/main.py >~/scripts/mijia-temperature/last.log 2>&1
 ```
+
+The published message will have this structure:
+```json
+{
+  "id": "mijia-sensor-1", 
+  "battery": 74, 
+  "temperature": 21.4, 
+  "humidity": 47.3
+}
+```