Setup Active Admin

:yellow_heart: I would recommend wrapping this `ENV['ADMIN_EMAILs']` concept in another module:

```ruby
# lib/admin.rb

module Admin
  def self.emails
    @emails ||= ENV['ADMIN_EMAILS'].strip.split(/\s+/)
  end
end
```

Usage: 

```ruby
def is_admin?
  self.email && Admin.emails.include?(self.email)
end
```

That way you don't have `ENV['ADMIN_EMAILS']` all over the app