document typst brand-logo and brand-logo-images

(cherry picked from commit 0e9318d)

Author: gordonwoodhull

docs/authoring/brand.qmd

@@ -695,6 +695,26 @@ For example, you could make a rectangle filled with your `primary` brand color:
 ```
 ````
 
+Brand logos are set in dictionaries called `brand-logo` and `brand-logo-images`.
+
+For example, you can write Typst code to insert an image using its resolved path and alt text from `brand.logo.images`:
+
+````{.markdown filename="document.qmd"}
+---
+format: typst
+brand:
+  logo:
+    images:
+      custom:
+        path: custom.png
+        alt: custom logo
+---
+
+```{=typst}
+#image(brand-logo-images.custom.path, alt=brand-logo-images.custom.alt)
+```
+````
+
 ### Lua API
 
 Filters and shortcodes can access brand values using the `brand` Lua module.