Add section for unpackaged apps (#4488)

* Add section for unpackaged apps

see http://task.ms/44790837

* fix some warnings found via build bot

fixing these
```
•	Line 66, Column 178:  [Warning] Link 'https://learn.microsoft.com/en-us/windows/win32/shell/appids#where-to-assign-an-appusermodelid' contains locale code 'en-us'. For localizability, remove 'en-us' from links to most Microsoft sites.
•	Line 66, Column 178:  [Suggestion] Absolute link 'https://learn.microsoft.com/en-us/windows/win32/shell/appids#where-to-assign-an-appusermodelid' will be broken in isolated environments. Replace with a relative link.
```

* Update windows-app-restore.md

* Update windows-app-restore.md

* Update windows-app-restore.md

windows/win32/msi/arpinstalllocation

* Update windows-app-restore.md

* Update windows-app-restore.md

ARPINSTALLLOCATION

* MSI -> Windows Installer

---------

Co-authored-by: Steven White <[email protected]>

Author: ChrisGuzak

hub/apps/develop/windows-app-restore.md

@@ -57,3 +57,11 @@ For more info about the best practices of storing app data, see [Store and retri
 ## Write user-generated content to Known Folders
 
 Windows introduced [known folders](/windows/win32/shell/known-folders) with Windows Vista. Since that time, users have come to expect that they can find the content they create with their apps in those locations. Writing user-generated content to those locations has the added benefit that OneDrive will back up those folders, if enabled, to ensure they're available to the user on their new PC (see [Back up your folders with OneDrive](https://support.microsoft.com/office/back-up-your-folders-with-onedrive-d61a7930-a6fb-4b95-b28a-6552e77c3057)). By using standard Windows APIs to write your user-generated content to the known folders, you're improving the user experience, and decreasing friction in adopting your app.
+
+## Best practices for unpackaged apps
+
+If you can't package your app, then be sure that your installer implements the recommendations below. That will ensure that it's possible to backup and restore the **Start** menu shortcuts that enable installing on a new machine that's restored from backup.
+
+* Make sure that your installer specifies an `InstallLocation` value in its uninstall registry key. When using [Windows Installer](/windows/win32/msi/windows-installer-portal) specify this using [ARPINSTALLLOCATION](/windows/win32/msi/arpinstalllocation). That's needed in order to enable the mapping of the **Start** menu shortcuts to the product.
+* Make sure that that location is specific to the product; usually the sub-directory under `C:\Program Files\<Publisher>\<Application>`.
+* Make sure that your **Start** menu shortcuts have machine-independent `System.AppUserModel.ID` (AMUID) values. That's best done by specifying them explicitly in the shortcut metadata. For more info, see [Where to Assign an AppUserModelID](/windows/win32/shell/appids#where-to-assign-an-appusermodelid).