Add comments to clarify about used design pattern

ILSpy/AssemblyTree/AssemblyTreeModel.cs

@@ -767,6 +767,7 @@ namespace ICSharpCode.ILSpy.AssemblyTree
 				}
 				else
 				{
+					// ensure that we are only connected once to the event, else we might get multiple notifications
 					ContextMenuProvider.ContextMenuClosed -= ContextMenuClosed;
 					ContextMenuProvider.ContextMenuClosed += ContextMenuClosed;
 				}