docs: add note and example on how to reuse a sidebar for a page

Author: mcanouil

docs/websites/website-navigation.qmd

@@ -377,7 +377,13 @@ website:
       title: "Reference"
       contents: 
         # navigation items
-    
+```
+
+To use a specific sidebar on a page or a group of pages, specify the `sidebar` ID in the front matter of the page or in the `_metadata.yml` file.
+For example, to include the tutorials sidebar, from the above example, on a page, add the following to the page's front matter:
+
+```yaml
+sidebar: tutorials
 ```
 
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