Add usage

README.md

@@ -9,6 +9,14 @@
 
 An easily configurable Docker image for running an Electrum server.
 
+## Usage
+
+```
+docker run -v /home/username/electrumx:/data -e DAEMON_URL=http://user:pass@host:port -e COIN=Bitcoin -p 50002:50002 lukechilds/electrumx
+```
+
+If there's an SSL certificate/key (`electrumx.crt`/`electrumx.key`) in the `/data` volume it'll be used. If not, one will be generated for you.
+
 ## License
 
 MIT © Luke Childs