Update upgrade process for supporting libraries

Added a reference to GitHub Copilot app modernization for library upgrades.

Author: wadepickett

aspnetcore/migration/fx-to-core/start.md

@@ -147,7 +147,7 @@ Depending on your application, you may also need to address:
 
 **Upgrade process for each library:**
 
-If you have supporting libraries in your solution that you will need to use for the routes you're migrating, they should be upgraded to .NET Standard 2.0, if possible. If libraries are unable to target .NET Standard, you can target .NET 8 or later either along with the .NET Framework target in the original project or in a new project alongside the original.
+If you have supporting libraries in your solution that you will need to use for the routes you're migrating, they should be upgraded to .NET Standard 2.0, if possible. [GitHub Copilot app modernization](/dotnet/core/porting/github-copilot-app-modernization/overview) can help you with this. If libraries are unable to target .NET Standard, you can target .NET 8 or later either along with the .NET Framework target in the original project or in a new project alongside the original.
 
 The [System.Web adapters](~/migration/fx-to-core/inc/systemweb-adapters.md) can be used in these libraries to enable support for <xref:System.Web.HttpContext> usage in class libraries. In order to enable <xref:System.Web.HttpContext> usage in a library: