Source code:
https://github.com/corsego/20-active_storage/
Docs:
https://edgeguides.rubyonrails.org/active_storage_overview.html

install active_storage, post has one avatar:
https://github.com/corsego/20-active_storage/commit/51a249ff58512284f492f5703da22f1f068ec1f9
post has many images:
https://github.com/corsego/20-active_storage/commit/f1775239f9c7471b0577fccd6e944964de383f10

0:00 The Problem
1:12 Install ActiveStorage
1:56 Has One Attached
4:30 Where are files stored?
06:00 Displaying images
08:19 Summary 1
09:59 Editing=Replacing Attachments
10:17 Has Many Attached
15:04 Next Steps