Added definition and explanation of environment variables (just http bind settings so far)

EnvironmentVariables.md

@@ -0,0 +1,28 @@
+# GoSmartKeyboard Environment Variables
+
+## HTTP Bind Settings
+
+
+GoSmartKeyboard supports both standard TCP sockets and unix sockets for the
+HTTP server.
+
+First, we check for a unix socket path.
+
+One should prefer a unix socket if their reverse proxy supports it and is on the
+same machine.
+
+--- unixSocketPath
+unixSocketPath, unixSocketPathExists := os.LookupEnv("KEYBOARD_UNIX_SOCKET_PATH")
+---
+
+If the unix socket path is set, we use it. Otherwise, we use the TCP socket.
+
+The TCP socket is configured by the following environment variables:
+
+--- TCPBindAddress
+tcpBindAddress, tcpBindAddressExists := os.LookupEnv("KEYBOARD_TCP_BIND_ADDRESS")
+---
+
+--- TCPBindPort
+tcpBindPort, tcpBindPortExists := os.LookupEnv("KEYBOARD_TCP_BIND_PORT")
+---