Docs: typos in mpm_r2s output description

https://quit.readthedocs.io/en/latest/Docs/Relaxometry.html#qi-mpm-r2s

<img width="1014" height="352" alt="Image" src="https://github.com/user-attachments/assets/c1051cb2-4df0-4218-8d67-1e96ddc19ade" />

I think this should probably be T1W signal and MTw signal respectively?