add exercise-finished readme template (#23)

* feat: add exercise finished message template for user completion

* Wording tweaks

---------

Co-authored-by: Christopher W. Blake <[email protected]>

Author: FidelusAleksander

markdown-templates/readme/congratulations.md

@@ -0,0 +1,19 @@
+# Congratulations! :tada:
+
+<img src="https://octodex.github.com/images/welcometocat.png" align="right" height="250px" />
+
+Yay **{{ login }}** you finished the exercise! Nice work :tada:
+
+If you would like to retrace your steps, you can always revisit the exercise.
+
+[![](https://img.shields.io/badge/Return%20to%20Exercise-%E2%86%92-1f883d?style=for-the-badge&logo=github&labelColor=197935)]({{{ issue_url }}})
+
+> [!TIP]
+> Mona won't grade you this time! 😉
+
+
+### Craving more? :raising_hand:
+
+Did you enjoy this practical style of learning? There's no better way to learn than building things, right?!
+
+Let's keep the momentum going! Head over to [GitHub Skills](https://skills.github.com) catalog to find another hands-on exercise. :rocket: