Added docs

README.md

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+# DSMR 2 MQTT bridge
+
+## Introduction
+
+This bridigng component reads Dutch Smart Meter Requirements (DSMR) telegrams and sends them to a MQTT broker using the [Homie convention](https://homieiot.github.io/). The component is written in Python and is based on the execelent work of others:
+
+* [DSMR Parser](https://github.com/ndokter/dsmr_parser)
+* [Homie4](https://github.com/mjcumming/homie4)
+
+![Works with Homie](https://homieiot.github.io/img/works-with-homie.png). 
+
+## Configuration
+
+Create some environment variables (e.g. with a .env file) to specify the required settings:
+
+```bash
+PYTHONPATH="."
+MQTT_HOST=mqtt.local
+DSMR_PORT=/dev/ttyUSB0
+```
+
+If you have forwared the raw serial signal through ser2net, you should use `DSMR_PORT=remote://<hostname>:<port>`, e.g.:
+
+```bash
+DSMR_PORT=remote://forwarding-pi.local:3333
+```
+
+If you use credentials to access the MQTT broker, then alsp specify:
+
+```bash
+MQTT_USERNAME=<mqtt-user>
+MQTT_PASSWORD=<mqtt_passwrd>
+```