the example code miss import torch

add import torch to handle error:
``` pipe = StableDiffusionPipeline.from_pretrained(model_id, scheduler=scheduler, revision="fp16", torch_dtype=torch.float16)
NameError: name 'torch' is not defined
```

README.md

@@ -46,6 +46,7 @@ Running the pipeline (if you don't swap the scheduler it will run with the defau
 
 ```python
 from diffusers import StableDiffusionPipeline, EulerDiscreteScheduler
+import torch
 
 model_id = "stabilityai/stable-diffusion-2-base"