Make LPIPS code example use the interval [-1, 1] (#1296)

* Make LPIPS code example use the interval [-1, 1]
* Apply suggestions from code review

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

src/torchmetrics/image/lpip.py

@@ -78,10 +78,11 @@ class LearnedPerceptualImagePatchSimilarity(Metric):
  >>> _ = torch.manual_seed(123)
  >>> from torchmetrics.image.lpip import LearnedPerceptualImagePatchSimilarity
  >>> lpips = LearnedPerceptualImagePatchSimilarity(net_type='vgg')
- >>> img1 = torch.rand(10, 3, 100, 100)
- >>> img2 = torch.rand(10, 3, 100, 100)
+ >>> # LPIPS needs the images to be in the [-1, 1] range.
+ >>> img1 = (torch.rand(10, 3, 100, 100) * 2) - 1
+ >>> img2 = (torch.rand(10, 3, 100, 100) * 2) - 1
  >>> lpips(img1, img2)
- tensor(0.3566, grad_fn=<SqueezeBackward0>)
+ tensor(0.3493, grad_fn=<SqueezeBackward0>)
  """
 
  is_differentiable: bool = True