feat(in-app-help): use preprocessed subtree data

docs/Release Notes/Release Notes/v0.92.8-beta.md

@@ -13,6 +13,9 @@
 *   Markdown export:
     *   Reduce extra whitespace between list items.
     *   Preserve include note.
+*   In-app help:
+    *   Document structure is now precalculated, so start-up time should be slightly increased.
+    *   Optimized the content in order to reduce the size on disk.
 
 ## 🌍 Internationalization