Update README.md (grafana#29075)

docs/README.md

@@ -22,6 +22,14 @@ Edit content in the `sources` directory.
 
 Use the Hugo shortcode [relref](https://gohugo.io/content-management/cross-references/#use-ref-and-relref) any time you are linking to other internal docs pages.
 
+Syntax is:
+```
+{{< relref "example.md" >}}
+```
+
+You might need to add more context for the link (containing folders and so on, `folder/example.md`) if Hugo says the relref is ambiguous. 
+
+
 ### Edit the side menu
 
 The side menu is automatically build from the file structure. Use the [weight](https://gohugo.io/templates/lists/#by-weight) front matter parameter to order pages.