docs: order the docs structure overview the same as the actual doc.

website/docs/user_guide/index.md

@@ -20,8 +20,8 @@ Have questions that you can't find the answer to in these docs? You can always t
 Our documentation is split into four parts, using the [Diataxis documentation framework](https://diataxis.fr/):
 - [tutorials and introductory material](#tutorials)
 - [how-to guides](#how-to-guides)
-- [topic guides](#topic-guides)
 - [reference documentation](#reference-documentation)
+- [topic guides](#topic-guides)
 
 ### Tutorials and introductory material {#tutorials}