Spell out Rails dependencies manually

Author: dhh

README.md

@@ -16,6 +16,15 @@ Importmap for Rails is automatically included in Rails 7+ for new applications,
 
 Note: In order to use JavaScript from Rails frameworks like Action Cable, Action Text, and Active Storage, you must be running Rails 7.0+. This was the first version that shipped with ESM compatible builds of these libraries.
 
+You can pin those libraries manually by relying on the compiled versions included in Rails like this:
+
+```ruby
+pin "@rails/actioncable", to: "actioncable.esm.js"
+pin "@rails/activestorage", to: "activestorage.esm.js"
+pin "@rails/actiontext", to: "actiontext.esm.js"
+pin "trix"
+```
+
 ## How do importmaps work?
 
 At their core, importmaps are essentially a string substitution for what are referred to as "bare module specifiers". A "bare module specifier" looks like this: `import React from "react"`. This is not compatible with the ES Module loader spec. Instead, to be ESM compatible, you must provide 1 of the 3 following types of specifiers: