Disable multithreading for MPS backend (#144)

* No multiprocessing on Apple MPS

Fixes #109.

* Document that Linux + GPU is recommended

casanovo/denovo/model_runner.py

@@ -386,7 +386,7 @@ def _get_devices(no_gpu: bool) -> Union[int, str]:
     """
     if not no_gpu and any(
         operator.attrgetter(device + ".is_available")(torch)()
-        for device in ["cuda", "backends.mps"]
+        for device in ("cuda",)
     ):
         return -1
     elif not (n_workers := utils.n_workers()):

docs/getting_started.md

@@ -74,6 +74,15 @@ Not all releases might have a model file included on the [Releases page](https:/
 
 ## Running Casanovo
 
+```{note}
+We recommend a Linux system with a dedicated GPU to achieve optimal runtime performance.
+Notably, Casanovo is restricted to single-threaded execution only on Windows and MacOS.
+```
+
+> **Warning**
+> Casanovo can currently crash if no GPU is available.
+> We are actively trying to fix this known issue.
+
 ### Sequence new mass spectra
 
 To sequence your own mass spectra with Casanovo, use the `denovo` mode: