add flow_design_styles.css to demo-app index.html

This closes #5
diff --git a/src/demo-app/index.html b/src/demo-app/index.html
index ce269ea..680a275 100644
--- a/src/demo-app/index.html
+++ b/src/demo-app/index.html
@@ -21,6 +21,7 @@
     <meta name='viewport' content='width=device-width, initial-scale=1'>
     <meta http-equiv='Content-Type' content='text/html; charset=UTF-8'/>
     <link rel="stylesheet" href="node_modules/@covalent/core/common/platform.css">
+    <link rel="stylesheet" href='node_modules/@nifi-fds/core/common/styles/css/flow-design-system.min.css'/>
     <link rel="stylesheet" href='demo-app/css/fds-demo.min.css'/>
     <link rel='stylesheet' href='node_modules/font-awesome/css/font-awesome.css'/>
 </head>