GitLab

* add a doc page for each pipeline under api/pipelines/stable_diffusion
* add pipeline examples to docstrings
* updated stable_diffusion_2 page
* updated default markdown syntax to list methods based on https://github.com/huggingface/diffusers/pull/1870


* add function decorator
Co-authored-by: yiyixuxu <yixu@Yis-MacBook-Pro.lan>
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>