Profile: document heap snapshot viewing tools (#55743)

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.