update README to cover new host/port options

Author: marcoow

README.md

@@ -36,7 +36,9 @@ const FastBootAppServer = require('fastboot-app-server');
 
 let server = new FastBootAppServer({
   distPath: 'dist',
-  gzip: true // Optional - Enables gzip compression.
+  gzip: true, // Optional - Enables gzip compression.
+  host: '0.0.0.0', // Optional - Sets the host the server listens on.
+  port: 4000 // Optional - Sets the port the server listens on (defaults to the PORT env var or 3000).
 });
 
 server.start();