packages,plugins: add package documentation

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

plugins/jenkins/api-report.md

@@ -153,6 +153,4 @@ export const LEGACY_JENKINS_ANNOTATION = 'jenkins.io/github-folder';
 //
 // @public (undocumented)
 export const Router: (_props: Props) => JSX.Element;
-
-// (No @packageDocumentation comment for this package)
 ```

plugins/jenkins/src/index.ts

@@ -14,6 +14,12 @@
  * limitations under the License.
  */
 
+/**
+ * A Backstage plugin that integrates towards Jenkins
+ *
+ * @packageDocumentation
+ */
+
 export {
   jenkinsPlugin,
   jenkinsPlugin as plugin,