packages,plugins: add package documentation

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/scaffolder/api-report.md

@@ -253,6 +253,4 @@ export const TextValuePicker: ({
   idSchema,
   placeholder,
 }: FieldProps<string>) => JSX.Element;
-
-// (No @packageDocumentation comment for this package)
 ```

plugins/scaffolder/src/index.ts

@@ -14,6 +14,12 @@
  * limitations under the License.
  */
 
+/**
+ * The Backstage plugin that helps you create new things
+ *
+ * @packageDocumentation
+ */
+
 export { scaffolderApiRef, ScaffolderClient } from './api';
 export type { ScaffolderApi } from './api';
 export {