message: Add documentation for readonly catalog
  This change contains documentation for the readonly configuration of the catalog
  (80e92b8f48843e079743944af6c20b3eaf42e3d9
diff: @@ -91,3 +91,28 @@ the catalog:
  catalog:
  rules: []
  ```
  +
  +## Readonly mode
  +
  +Processors provides a good way to automate ingestion of entities when combined
  +with [Static Location Configuration](#static-location-configuration) or a
  +discovery processor like
  +[GitHub Discovery](../../integrations/github/discovery.md). To enforce usage of
  +processors to locate entities we can configure the catalog into `readonly` mode.
  +This configuration disables the mutating backend catalog APIs and disallows
  +users from registering new entities at run-time.
  +
  +```yaml
  +catalog:
  + readonly: true
  +```
  +
  +> **Note that any plugin relying on the catalog API for creating, updating and
  +> deleting entities will not work in this mode.**
  +
  +A common use case for this configuration is when organizations have a remote
  +source that should be mirrored into backstage. If we want backstage to be a
  +mirror of this remote source we cannot allow users to also register entities
  +with e.g.
  +[catalog-import](https://github.com/backstage/backstage/tree/master/plugins/catalog-import)
  +plugin.
  