docs: recommend subdirectory for userData to avoid Chromium conflicts (#50563)

Fixes #45414

Storing files directly in the userData root can cause naming conflicts
with Chromium's own subdirectories (Cache, GPUCache, Local Storage, etc.).
Added a recommendation to use a subdirectory such as
path.join(app.getPath('userData'), 'my-app-data') instead.

Notes: no-notes

docs/api/app.md

@@ -615,7 +615,11 @@ Returns `string` - The current application directory.
     by default is the `appData` directory appended with your app's name. By
     convention files storing user data should be written to this directory, and
     it is not recommended to write large files here because some environments
-    may backup this directory to cloud storage.
+    may backup this directory to cloud storage. It is recommended to store
+    app-specific files within a subdirectory of `userData` (e.g.,
+    `path.join(app.getPath('userData'), 'my-app-data')`) rather than directly
+    in `userData` itself, to avoid naming conflicts with Chromium's own
+    subdirectories (such as `Cache`, `GPUCache`, and `Local Storage`).
   * `sessionData` The directory for storing data generated by `Session`, such
     as localStorage, cookies, disk cache, downloaded dictionaries, network
     state, DevTools files. By default this points to `userData`. Chromium may