docs: adds an advanced topics section

Author: iOvergaard

16/umbraco-cms/customizing/foundation/fetching-data/README.md

@@ -38,10 +38,12 @@ The HTTP Client is a wrapper around the Fetch API that provides a more convenien
 
 ## Handle Requests
 
-### [Executing Requests](try-execute.md)
+## [Executing Requests](try-execute.md)
 
 Executing the request is the next step after fetching data. You can use the `tryExecute` function to handle errors and refresh the token if it is expired.
 
+## Advanced Topics
+
 ### [Custom Generated Client](custom-generated-client.md)
 
 It can be useful to generate a custom client for your API. This can save you a lot of time and effort when working with custom API controllers.