Add NuGet guidance to CS1061 compiler error documentation

Co-authored-by: BillWagner <[email protected]>

Author: Copilot

.gitignore

@@ -63,3 +63,6 @@ BenchmarkDotNet.Artifacts
 
 # ReplayCheck (temporary)
 .replaycheck/
+
+# Node.js dependencies
+node_modules/

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

@@ -49,6 +49,7 @@ public class Program
 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).
+4. 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