Update README.md

Add `npm run dev` information

Author: shockey

README.md

@@ -26,6 +26,8 @@ If you have Node.js and npm installed, you can run `npm start` to spin up a stat
 
 Otherwise, you can open `index.html` directly from your filesystem in your browser.
 
+If you'd like to make code changes to Swagger-Editor, you can start up a Webpack hot-reloading dev server via `npm run dev`. 
+
 ##### Browser support
 
 Swagger UI works in the latest versions of Chrome, Safari, Firefox, Edge and IE11.