Use config file for default docker cmd

Dockerfile

@@ -13,4 +13,4 @@ RUN apt-get update && \
 COPY hc2mqtt hc-login HCDevice.py HCSocket.py HCxml2json.py ./
 
 ENTRYPOINT ["python3"]
-CMD ["hc2mqtt", "/config/config.json"]
+CMD ["hc2mqtt", "--config", "/config/config.ini"]

README.md

@@ -47,6 +47,7 @@ hc-login $USERNAME $PASSWORD > config/devices.json
 or
 
 ```bash
+docker-compose build
 docker-compose run -T app hc-login $USERNAME $PASSWORD > config/devices.json
 ```
 
@@ -84,6 +85,12 @@ mqtt_clientname="hcpy"
 hc2mqtt --config config/config.ini
 ```
 
+or
+
+```bash
+docker-compose up
+```
+
 This tool will establish websockets to the local devices and
 transform their messages into MQTT JSON messages.  The exact
 format is likely to change; it is currently a thin translation