feat(semantic-layer): guide semantic layer setup

docs/admin_docs/configuration/configuring-superset.mdx

@@ -869,6 +869,19 @@ SUPERSET_DASHBOARD_POSITION_DATA_LIMIT = 131072  # double the default
 
 Alternatively, split a very large dashboard into several smaller ones. Note that this check is enforced when saving layout edits in the UI; a dashboard imported from a ZIP with an oversized layout will load and render, but cannot be edited and re-saved until the limit is raised.
 
+## Semantic layer setup documentation
+
+Set `SEMANTIC_LAYER_DOCUMENTATION_URL` in `superset_config.py` to an absolute
+HTTP or HTTPS URL for your deployment's semantic layer setup guide. The New
+Semantic Layer and Add Semantic View dialogs show this optional link. It opens
+in a new tab. Leave the setting as `None` (the default) to hide the link. Invalid
+URLs and URLs with username/password userinfo are omitted from the page bootstrap
+rather than partially sanitized; the server logs a warning without the URL value.
+
+This setting does not change the main documentation menu's `DOCUMENTATION_URL`,
+install providers, grant permissions, or enable the `SEMANTIC_LAYERS` feature.
+Provider setup descriptions come from each registered provider's metadata.
+
 :::resources
 
 - [Blog: Feature Flags in Apache Superset](https://preset.io/blog/feature-flags-in-apache-superset-and-preset/)