update readme

[MilesWilde]

Hello,

I believe these values work for image prompt in the current version

I tested with style_selections, aspect_ratios_selection, prompt, aspect_ratios_selection, image_seed. I assume the others work since they are part of the parser in fooocusapi\api_utils.py#req_to_params(req: Text2ImgRequest)

[mrhan1993]

In fact, all the generation interfaces inherit from text2image, so the repetitive parts are not specifically explained. If you believe that it is necessary to make changes, you can add a public explanation, which can greatly reduce repetition and document length.