fix pix2pix docs (#2290)

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_instruct_pix2pix.py

@@ -147,7 +147,7 @@ class StableDiffusionInstructPix2PixPipeline(DiffusionPipeline):
         Function invoked when calling the pipeline for generation.
 
         Args:
-             prompt (`str` or `List[str]`, *optional*):
+            prompt (`str` or `List[str]`, *optional*):
                 The prompt or prompts to guide the image generation. If not defined, one has to pass `prompt_embeds`.
                 instead.
             image (`PIL.Image.Image`):