packages,plugins: add package documentation

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

plugins/todo-backend/api-report.md

@@ -131,6 +131,4 @@ export interface TodoService {
 // Warnings were encountered during analysis:
 //
 // src/service/types.d.ts:9:9 - (ae-forgotten-export) The symbol "Fields" needs to be exported by the entry point index.d.ts
-
-// (No @packageDocumentation comment for this package)
 ```

plugins/todo-backend/src/index.ts

@@ -14,5 +14,11 @@
  * limitations under the License.
  */
 
+/**
+ * A Backstage backend plugin that lets you browse TODO comments in your source code
+ *
+ * @packageDocumentation
+ */
+
 export * from './lib';
 export * from './service';