add how to use it

Author: mattiaerre

README.md

@@ -2,9 +2,12 @@
 
 OpenComponent Registry GraphQL Express middleware.
 
-```bash
-yarn
-yarn test
+## How to use it w/in your Registry
+
+```javascript
+const middleware = require('oc-registry-graphql-express-middleware'); // once available on npm
+
+registry.app.use('/graphql', middleware({ baseUrl: 'http://localhost:3000/', graphiql: true }));
 ```
 
 ![query-registry](query-registry.png "query-registry")