Update README

Author: htdvisser

README.md

@@ -2,11 +2,80 @@
 
 [![Build Status](https://travis-ci.org/TheThingsNetwork/gateway-connector-bridge.svg?branch=master)](https://travis-ci.org/TheThingsNetwork/gateway-connector-bridge) [![Coverage Status](https://coveralls.io/repos/github/TheThingsNetwork/gateway-connector-bridge/badge.svg?branch=master)](https://coveralls.io/github/TheThingsNetwork/gateway-connector-bridge?branch=master)
 
-## Getting Started
+## Installation
+
+Download precompiled binaries for [64 bit Linux][download-linux-amd64], [32 bit Linux][download-linux-386], [ARM Linux][download-linux-arm], [macOS][download-darwin-amd64], [64 bit Windows][download-windows-amd64], [32 bit Windows][download-windows-386].
+
+[download-linux-amd64]: https://ttnreleases.blob.core.windows.net/gateway-connector-bridge/master/gateway-connector-bridge-linux-amd64.zip
+[download-linux-386]: https://ttnreleases.blob.core.windows.net/gateway-connector-bridge/master/gateway-connector-bridge-linux-386.zip
+[download-linux-arm]: https://ttnreleases.blob.core.windows.net/gateway-connector-bridge/master/gateway-connector-bridge-linux-arm.zip
+[download-darwin-amd64]: https://ttnreleases.blob.core.windows.net/gateway-connector-bridge/master/gateway-connector-bridge-darwin-amd64.zip
+[download-windows-amd64]: https://ttnreleases.blob.core.windows.net/gateway-connector-bridge/master/gateway-connector-bridge-windows-amd64.exe.zip
+[download-windows-386]: https://ttnreleases.blob.core.windows.net/gateway-connector-bridge/master/gateway-connector-bridge-windows-386.exe.zip
+
+Other requirements are:
+
+- [Redis](http://redis.io/download)
+- An MQTT Broker (see also the [Security](#security) section)
+
+## Usage
+
+```
+Usage:
+  gateway-connector-bridge [flags]
+
+Flags:
+      --account-server string    Use an account server for exchanging access keys (default "https://account.thethingsnetwork.org")
+      --amqp stringSlice         AMQP Broker to connect to (user:pass@host:port; disable with "disable")
+      --debug                    Print debug logs
+      --http-debug-addr string   The address of the HTTP debug server to start
+      --id string                ID of this bridge
+      --log-file string          Location of the log file
+      --mqtt stringSlice         MQTT Broker to connect to (user:pass@host:port; disable with "disable") (default [guest:guest@localhost:1883])
+      --redis                    Use Redis auth backend (default true)
+      --redis-address string     Redis host and port (default "localhost:6379")
+      --redis-db int             Redis database
+      --redis-password string    Redis password
+      --root-ca-file string      Location of the file containing Root CA certificates
+      --status-addr string       Address of the gRPC status server to start
+      --ttn-router stringSlice   TTN Router to connect to (default [discover.thethingsnetwork.org:1900/ttn-router-eu])
+      --workers int              Number of parallel workers (default 1)
+```
+
+For running in Docker, please refer to [`docker-compose.yml`](docker-compose.yml).
+
+## Protocol
+
+The Things Network's `gateway-connector` protocol sends protocol buffers over MQTT.
+
+- Connect to MQTT with your gateway's ID as username and Access Key as password.
+  - On MQTT brokers that don't support authentication, you can connect without authentication.
+- After connect: send [`types.ConnectMessage`](types/types.proto) on topic `connect`.
+  - Supply the gateway's ID and Access Key to authenticate with the backend
+- On disconnect: send [`types.DisconnectMessage`](types/types.proto) on topic `disconnect`.
+  - Supply the same ID and Access Key as in the `ConnectMessage`.
+  - Use the "will" feature of MQTT to send the `DisconnectMessage` when the gateway unexpectedly disconnects.
+- On uplink: send [`router.UplinkMessage`](https://github.com/TheThingsNetwork/ttn/blob/develop/api/router/router.proto) on topic `<gateway-id>/up`.
+- For downlink: subscribe to topic `<gateway-id>/down` and receive [`router.DownlinkMessage`](https://github.com/TheThingsNetwork/ttn/blob/develop/api/router/router.proto).
+- On status: send [`gateway.Status`](https://github.com/TheThingsNetwork/ttn/blob/develop/api/gateway/gateway.proto) on topic `<gateway-id>/status`.
+
+## Security
+
+⚠️ MQTT brokers should support authentication and access control:
+
+- The `connect`, `disconnect`, `<gateway-id>/up`, `<gateway-id>/status` topics **must only allow**
+  - **publish** for authenticated gateways with `<gateway-id>`.
+  - **subscribe** for the bridge.
+- The `<gateway-id>/down` topics **must only allow**
+  - **publish** for the bridge.
+  - **subscribe** for authenticated gateways with `<gateway-id>`.
+
+## Development
 
 - Make sure you have [Go](https://golang.org) installed (version 1.7 or later).
-- Set up your [Go environment](https://golang.org/doc/code.html#GOPATH)
-- Make sure you have [RabbitMQ](https://www.rabbitmq.com/download.html) and its [MQTT plugin](https://www.rabbitmq.com/mqtt.html) **installed** and **running**.  
+- Set up your [Go environment](https://golang.org/doc/code.html#GOPATH).
+- Make sure you have [Redis](http://redis.io/download) **installed** and **running**.
+- Make sure you have [RabbitMQ](https://www.rabbitmq.com/download.html) and its [MQTT plugin](https://www.rabbitmq.com/mqtt.html) **installed** and **running**.
 - Fork this repository on Github
 - `git clone git@github.com:YOURUSERNAME/gateway-connector-bridge.git $GOPATH/src/github.com/TheThingsNetwork/gateway-connector-bridge.git`
 - `cd $GOPATH/src/github.com/TheThingsNetwork/gateway-connector-bridge`