enhance(ui): custom docs url

add note about customizing VELA_DOCS_URL

content/installation/ui/reference/_index.md

@@ -44,6 +44,8 @@ The variable can be provided as a `string`.
 
 {{% alert title="Note:" color="primary" %}}
 This variable has a default value of `https://go-vela.github.io/docs/`.
+
+Please note that this variable is used in deep links throughout the UI. Customizing this value assumes the target location utilizes the same URL structure as the official docs at the default location.
 {{% /alert %}}
 
 ### VELA_FEEDBACK_URL
@@ -80,4 +82,4 @@ The variable can be provided as an `integer`.
 This variable has a default value of `30`.
 
 This variable should match [the `VELA_MAX_BUILD_LIMIT` variable](/docs/installation/server/reference/#vela_max_build_limit) provided to the server.
-{{% /alert %}}
+{{% /alert %}}