Add course on free-courses-id.md (#5620)

courses/free-courses-id.md

@@ -101,6 +101,7 @@
 
 * [Flutter Membangun Website](https://buildwithangga.com/kelas/flutter-membangun-website-sederhana?thumbnail=nk4neM2UyG.110&main_leads=browse) - BuildWithAngga
 * [Flutter Tutorial (Flutter Fundamentals)](https://www.youtube.com/playlist?list=PLZQbl9Jhl-VACm40h5t6QMDB92WlopQmV) - Erico Darmawan Handoyo
+* [STUDI KASUS FLUTTER + GETX + FIREBASE [ CHAT APPS 2021 ]](https://www.youtube.com/playlist?list=PL7jdfftn7HKt6wPnVXoXgserU14d_ACA-) - Sandikha Rahardi, Kuldii Project (YouTube)
 * [Tutorial Flutter](https://www.youtube.com/playlist?list=PL0-7Xi0GB3teRqkuBusUEcVrP6OlYpD9w) - idr corner