Docs vuepress (#476)

Convert docs to vuepress

docs/prerequisites/broker.md

@@ -0,0 +1,20 @@
+# Broker
+The broker will act as an intermediary between OpenMQTTGateway and your [controller](/prerequisites/controller), it can be seen as a centralized hub at the heart of your automation system. It carry on messages following a publish / subscribe mechanism.
+
+All the events or commands could pass by the broker.
+
+There is many choice of brokers, here is some of the most populars:
+* [Mosquitto](https://mosquitto.org/) (Open source)
+* [Moquette](https://moquette-io.github.io/moquette/) (Open source)
+* [HiveMQ](https://www.hivemq.com/hivemq/features/)
+* Embedded MQTT brokers (Home Assistant and OpenHAB)
+
+This [wikipedia list](https://en.wikipedia.org/wiki/Comparison_of_MQTT_implementations) gives you more details about the different choices you have.
+This [github list](https://github.com/mqtt/mqtt.github.io/wiki/libraries) seems to be the most exhaustive ones.
+Here is also some [idea of criterias](https://www.hivemq.com/blog/top-10-mqtt-broker-criteria/) from HiveMQ.
+
+Once your broker installed it can be interesting to see the traffic passing to it and to publish data, so as to do that there is several tools available:
+* [MQTT Explorer](http://mqtt-explorer.com/)
+* [HIVE MQ Web client](https://github.com/hivemq/hivemq-mqtt-web-client)
+* [MQTT FX](https://mqttfx.jensd.de/)
+