add section for moving public directory in upgrade guide (#191)

pages/docs/v3/updating/3-0.md

@@ -135,6 +135,28 @@ Do the following for your Xcode project and app target: open the **Build Setting
 
 If your app is not already using Swift 5, open the **Build Settings** tab in your Xcode target, then change **Swift Language Version** to **Swift 5** under the **Swift Compiler - Language** section.
 
+### Move `public` into the iOS target directory
+
+It is recommended in Capacitor 3 to move the `ios/App/public` directory into `ios/App/App/public`. This can be achieved in Xcode:
+
+**Remove existing `public` folder**
+
+1. Expand the file tree under the `App` project, then the `App` group, and select the `public` folder.
+1. Right-click on **Delete**. When prompted to delete the folder or just remove the reference, select **Move to Trash**.
+
+![delete public folder](/assets/img/docs/ios/xcode-public-delete-folder.png)
+
+**Recreate `public` in the new location**
+
+1. Right-click on the `App` group inside the `App` project and click **Add Files to "App"...**
+1. Leave the default options (ensuring to create folder references, not groups and to add to the `App` target).
+1. Click **New Folder**, name it "public".
+1. Click **Create**, then **Add**.
+
+![recreate public folder](/assets/img/docs/ios/xcode-public-new-folder.png)
+
+It may look the same in Xcode, but the new `public` folder should now be relative to the `App` group, not the project root.
+
 ### Update the Capacitor iOS platform
 
 ```bash