Install instructions missing transformers

[wrexbe]

The installing instructions say to install diffusers, but not anything else.

So the first time people try the example they are going to get this error:
ImportError:
StableDiffusionPipeline requires the transformers library but it was not found in your environment. You can install it with pip: pip install transformers

Can you include all install instructions needed to run the example programs in the documentation?

[patrickvonplaten]

Yes ok for me! Would you like to open a PR ?