DOC: Use enumerate in extract example (#2727)

docs/user/extract-images.md

@@ -12,12 +12,10 @@ from pypdf import PdfReader
 reader = PdfReader("example.pdf")
 
 page = reader.pages[0]
-count = 0
 
-for image_file_object in page.images:
+for count, image_file_object in enumerate(page.images):
     with open(str(count) + image_file_object.name, "wb") as fp:
         fp.write(image_file_object.data)
-        count += 1
 ```
 
 # Other images