Document kit cases

We should document how cases are assembled and which parts are needed.

<details><summary>Parts</summary>
<p>

<img width="2084" height="4624" alt="Image" src="https://github.com/user-attachments/assets/e3479e7c-b468-4a2b-ad39-de90a66a7902" />

</p>
</details> 

