[docs] Add a note of `_keep_in_fp32_modules` (#11851)

* update

* Update docs/source/en/using-diffusers/schedulers.md
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update schedulers.md

---------
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

docs/source/en/using-diffusers/schedulers.md

@@ -242,3 +242,15 @@ unet = UNet2DConditionModel.from_pretrained(
 )
 unet.save_pretrained("./local-unet", variant="non_ema")
 ```
+
+Use the `torch_dtype` argument in [`~ModelMixin.from_pretrained`] to specify the dtype to load a model in.
+
+```py
+from diffusers import AutoModel
+
+unet = AutoModel.from_pretrained(
+    "stabilityai/stable-diffusion-xl-base-1.0", subfolder="unet", torch_dtype=torch.float16
+)
+```
+
+You can also use the [torch.Tensor.to](https://docs.pytorch.org/docs/stable/generated/torch.Tensor.to.html) method to convert to the specified dtype on the fly. It converts *all* weights unlike the `torch_dtype` argument that respects the `_keep_in_fp32_modules`. This is important for models whose layers must remain in fp32 for numerical stability and best generation quality (see example [here](https://github.com/huggingface/diffusers/blob/f864a9a352fa4a220d860bfdd1782e3e5af96382/src/diffusers/models/transformers/transformer_wan.py#L374)).