doc: heap snapshot viewing

Say that:
* VS Code may be used for viewing heap snapshots. Important because
  Chromium currently may *not* be used for this on Julia v1.11 and up:
  JuliaLang#54414
* Firefox can't be used.

stdlib/Profile/docs/src/index.md

@@ -155,3 +155,8 @@ julia> Profile.HeapSnapshot.assemble_snapshot("snapshot", "snapshot.heapsnapshot
 
 The resulting heap snapshot file can be uploaded to chrome devtools to be viewed.
 For more information, see the [chrome devtools docs](https://developer.chrome.com/docs/devtools/memory-problems/heap-snapshots/#view_snapshots).
+An alternative for analyzing Chromium heap snapshots is with the VS Code extension
+`ms-vscode.vscode-js-profile-flame`.
+
+The Firefox heap snapshots are of a different format, and Firefox currently may
+*not* be used for viewing the heap snapshots generated by Julia.