Update README.md

Update the install instruction

README.md

@@ -87,7 +87,7 @@ Which should give you an image like below:
 
 ### Using Controlnets in Diffusers
 
-Make sure you upgrade to the latest version of diffusers: `pip install -U diffusers`. And then you can run:
+Make sure you upgrade to the latest version of diffusers: `pip install git+https://github.com/huggingface/diffusers`. And then you can run:
 
 ```python
 import torch