message: Add example of visibility of config values
  Emphasize how to set config visibility in the docs with an example.
diff: @@ -93,6 +93,21 @@ declare the visibility of a leaf node of `type: "string"`.
  | `backend` | (Default) Only in backend |
  | `secret` | Only in backend and may be excluded from logs for security reasons |
  +You can set visibility with an `@visibility` comment in the `Config` Typescript
  +interface.
  +
  +```ts
  +export interface Config {
  + app: {
  + /**
  + * Frontend root URL
  + * @visibility frontend
  + */
  + baseUrl: string;
  + };
  +}
  +```
  +
  ## Validation
  Schemas can be validated using the `backstage-cli config:check` command. If you
  