add link to advanced typst brand yaml doc

Author: gordonwoodhull

docs/authoring/brand.qmd

@@ -540,6 +540,8 @@ For example, you could make a rectangle filled with your `primary` brand color:
 ```
 ````
 
+See [the Advanced documentation](/docs/advanced/typst/brand-yaml.qmd) for more details on the implementation, and troubleshooting tips.
+
 ### Lua API
 
 Filters and shortcodes can access brand values using the `brand` Lua module.