added redis disclaimer for npm start

README.md

@@ -174,6 +174,8 @@ $ npm run start:dev
 $ npm run start:prod
 ```
 
+**Note that you need to have redis running locally in order to run the app**
+
 After starting the app, navigate to the displayed URL (`https://localhost:3000`)
 in order to check out the API docs and the basic single-page screenshotting
 application.