docs(nav): add cookbook to top-level toctree

mschaepers · mschaepers · commit 973600ddf4b2 · 2026-05-11T00:56:21.000+02:00
diff --git a/docs/index.md b/docs/index.md
@@ -238,6 +238,7 @@ section_config
 section_core
 section_thermal
 study_cases/index
+cookbook/index
 section_reference
 
 ```
