docs: add a screenshot of an example pull request

Author: hasundue

README.md

@@ -7,6 +7,10 @@
 A GitHub Action to update dependencies in Deno projects with
 [molt](https://github.com/hasundue/molt).
 
+## Example
+
+![image](https://github.com/hasundue/molt-action/assets/309723/92246a9c-c86a-4dee-bef8-468ae8ac448d)
+
 ## Usage
 
 ```yaml