Merge pull request #36060 from st0012/fix-35602-doc

Add ActionController::Caching into api app's document [ci skip]

guides/source/api_app.md

@@ -420,6 +420,15 @@ Some common modules you might want to add:
 - `ActionController::MimeResponds`: Support for `respond_to`.
 - `ActionController::Cookies`: Support for `cookies`, which includes
   support for signed and encrypted cookies. This requires the cookies middleware.
+- `ActionController::Caching`: Support view caching for the API controller. Please notice that
+  you will need to manually specify cache store inside the controller like:
+  ```ruby
+  class ApplicationController < ActionController::API
+    include ::ActionController::Caching
+    self.cache_store = :mem_cached_store
+  end
+  ```
+  Rails does *not* pass this configuration automatically.
 
 The best place to add a module is in your `ApplicationController`, but you can
 also add modules to individual controllers.