Add NuGet package guidance to CS1061 compiler error documentation (#47961)

Author: Copilot

docs/csharp/language-reference/compiler-messages/cs1061.md

@@ -46,9 +46,10 @@ public class Program
 
 ## To correct this error
 
-1. Make sure you typed the member name correctly.
-2. If you have access to modify this class, you can add the missing member and implement it.
-3. If you don't have access to modify this class, you can add an [extension method](../../programming-guide/classes-and-structs/extension-methods.md).
+- Make sure you typed the member name correctly.
+- If you have access to modify this class, you can add the missing member and implement it.
+- If you don't have access to modify this class, you can add an [extension method](../../programming-guide/classes-and-structs/extension-methods.md).
+- If the member you're trying to access should exist but doesn't, you might be missing a required NuGet package. Search [NuGet.org](https://www.nuget.org/) to find packages that contain the missing member.
 
 ## See also