How to use Active Storage in Rails

What'll we do:

Introduction about Active Storage.
Create a new Rails application and CRUD for Post.
Setup Active Storage + Amazon S3 Service
Using Active Storage to:
- Upload Images for Post
- Upload a File (PDF or Video) for Post
Conclusion

Name		Name	Last commit message	Last commit date
Latest commit History 8 Commits
app		app
bin		bin
config		config
db		db
lib		lib
log		log
public		public
storage		storage
test		test
tmp		tmp
vendor		vendor
.gitignore		.gitignore
.ruby-gemset		.ruby-gemset
.ruby-version		.ruby-version
Gemfile		Gemfile
Gemfile.lock		Gemfile.lock
README.md		README.md
Rakefile		Rakefile
config.ru		config.ru
package.json		package.json