Update free-courses-vi.md (#4935)

free-courses-vi.md

@@ -72,6 +72,7 @@
 ### Bootstrap
 
 * [Twitter Bootstrap](https://www.codehub.com.vn/Twitter-Bootstrap)
+* [Tự học Bootstrap 4 cơ bản](https://www.youtube.com/playlist?list=PLQi-dJ8Gqv2i1NHD8f-E2w-zrrr9G7HUJ) - VIETPRO
 
 
 ### C