Update README

Revision of the previous commit to make it less misleading and mention the option of using .bin files

Fix ugly img2img resize options

Fixes for mps/Metal: use of seeds, img2img, CodeFormer

- small update to reflect the revised commit for gradio authentication

 Instance of CUDA out of memory on a low-res batch, even with --opt-split-attention-v1 (found cause) #255

- Documented a couple of new optional flags
- Added a link to a third party repository of embeddings
- Reworded a few parts
- Fixed some typos

Update cross attention to the newest version

Channels last support

Add --gradio-auth command line argument to enable Gradio authentication

Allows you to pass in Gradio authentication like:
`--auth username:password`
Supports multiple sets of credentials by comma-delimiting, like:
`--auth user1:pass1,user2:pass3`...