Update Podfile in template (#35931)

Summary:
Added comment on Podfile under template directory.
I'm working with monorepo and didn't realize it easily to specify the path for react_native_post_install, so I thought it would be better to add this comment.

## Changelog

[IOS] [ADDED] - add comments for specifying the path to React Native

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Pull Request resolved: #35931

Reviewed By: cipolleschi

Differential Revision: D42673707

Pulled By: jacdebug

fbshipit-source-id: 39e424a051d238f6dad42cb0b7748d4f4c400787

template/ios/Podfile

@@ -47,10 +47,9 @@ target 'HelloWorld' do
   end
 
   post_install do |installer|
+    # https://github.com/facebook/react-native/blob/main/scripts/react_native_pods.rb#L197-L202
     react_native_post_install(
       installer,
-      # Set `mac_catalyst_enabled` to `true` in order to apply patches
-      # necessary for Mac Catalyst builds
       :mac_catalyst_enabled => false
     )
     __apply_Xcode_12_5_M1_post_install_workaround(installer)