docs: add note about gallery listing example

Author: mcanouil

docs/websites/website-listings-custom.qmd

@@ -132,13 +132,17 @@ where the contents of `items.yml` is:
 Portions of this website are built using custom listings. The best place to start is with [our gallery](/docs/gallery/index.qmd), which is a listing built using a custom template and a metadata file. You can view the source code used to create the gallery page in our [Github repository](https://github.com/quarto-dev/quarto-web).
 
 | File                                                                                       | Description                                                                          |
-|-------------------------------------|-----------------------------------|
+|--------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------|
 | [gallery.yml](https://github.com/quarto-dev/quarto-web/blob/main/docs/gallery/gallery.yml) | The metadata that controls what items are displayed in the gallery listing.          |
 | [gallery.ejs](https://github.com/quarto-dev/quarto-web/blob/main/docs/gallery/gallery.ejs) | The template used to display the items on the page.                                  |
 | [index.qmd](https://github.com/quarto-dev/quarto-web/blob/main/docs/gallery/index.qmd)     | The Quarto document that configures and positions the listing in the `#gallery` div. |
 
 : {tbl-colwidths="\[30,70\]"}
 
+::: {.callout-note}
+Note that the `gallery.ejs` template does not allow its content to be read as Markdown.
+:::
+
 ## Sorting, Filtering, and Pagination
 
 By default, sorting, filtering, and pagination are disabled for custom listings templates, but with some simple changes to your template and listing options, you can add this capability to your custom listing. To do this, you need to include the following three things in your custom template: