fix docs: change sample to images (huggingface#613)

the result of running the pipeline is stored in StableDiffusionPipelineOutput.images

Author: AbdullahAlfaraj

src/diffusers/pipelines/stable_diffusion/README.md

@@ -67,7 +67,7 @@ pipe = pipe.to("cuda")
 
 prompt = "a photo of an astronaut riding a horse on mars"
 with autocast("cuda"):
-    image = pipe(prompt).sample[0]  
+    image = pipe(prompt).images[0]  
 
 image.save("astronaut_rides_horse.png")
 ```
@@ -89,7 +89,7 @@ pipe = StableDiffusionPipeline.from_pretrained(
 
 prompt = "a photo of an astronaut riding a horse on mars"
 with autocast("cuda"):
-    image = pipe(prompt).sample[0]  
+    image = pipe(prompt).images[0]  
 
 image.save("astronaut_rides_horse.png")
 ```
@@ -115,7 +115,7 @@ pipe = StableDiffusionPipeline.from_pretrained(
 
 prompt = "a photo of an astronaut riding a horse on mars"
 with autocast("cuda"):
-    image = pipe(prompt).sample[0]  
+    image = pipe(prompt).images[0]  
 
 image.save("astronaut_rides_horse.png")
 ```