Add comments to nuget.config file restore

Author: tamasvajk

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetPackages.cs

@@ -267,8 +267,8 @@ public void Dispose()
                 using (var backup = File.OpenRead(backupNugetConfig))
                 using (var current = File.OpenWrite(nugetConfigPath))
                 {
-                    current.SetLength(0);
-                    backup.CopyTo(current);
+                    current.SetLength(0);   // Truncate file
+                    backup.CopyTo(current); // Restore original content
                 }
 
                 logger.LogInfo("Deleting backup nuget.config file");