vscode: add backports notice

pkgs/applications/editors/vscode/vscode.nix

@@ -19,6 +19,8 @@ in
     # The update script doesn't correctly change the hash for darwin, so please:
     # nixpkgs-update: no auto update
 
+    # Please backport all compatible updates to the stable release.
+    # This is important for the extension ecosystem.
     version = "1.43.0";
     pname = "vscode";