chore: add server hint in order to run the apps

Author: Zdravko

README.md

@@ -73,6 +73,7 @@ var params = [
 		];
 task = session.multipartUpload(params, request);
 ```
+> To get advantage of the demo apps and test the functionality, you will have to start the server from `demo-server` folder part of the repository. To do so, execute `cd demo-server && npm run start` command in a terminal.
 
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