[DOCS] `/waveorder/stokes` docstring doesn't render cleanly

Moved from @srivarra's comment: https://github.com/mehta-lab/waveorder/pull/461#discussion_r2274686138. Minor reformatting should fix this.

<img width="1118" height="1214" alt="Image" src="https://github.com/user-attachments/assets/3b4f968a-9b7d-47e9-b49d-7868f6e351a2" />