build: add comment about torchsde to pyproject

Author: psychedelicious

pyproject.toml

@@ -47,7 +47,7 @@ dependencies = [
   "safetensors",
   "spandrel==0.3.4",
   "torch~=2.6.0",                         # torch and related dependencies are loosely pinned, will respect requirement of `diffusers[torch]`
-  "torchsde",
+  "torchsde",                             # diffusers needs this for SDE solvers, but it is not an explicit dep of diffusers
   "torchvision",
   "transformers",