Add torch import to diffusers example

The example is missing the import of torch to be run 😌

README.md

@@ -43,6 +43,7 @@ pip install diffusers transformers accelerate scipy safetensors
 Running the pipeline (if you don't swap the scheduler it will run with the default DDIM, in this example we are swapping it to DPMSolverMultistepScheduler):
 
 ```python
+import torch
 from diffusers import StableDiffusionPipeline, DPMSolverMultistepScheduler
 
 model_id = "stabilityai/stable-diffusion-2-1"