Fix #2814: Remove Markdown backticks, use RST syntax for code block

Author: Rachel0619

beginner_source/introyt/introyt1_tutorial.py

@@ -304,7 +304,8 @@ def num_flat_features(self, x):
 #    standard deviations (second tuple) of the rgb values of the images in
 #    the dataset. You can calculate these values yourself by running these
 #    few lines of code:
-#          ```
+#          ::
+#
 #           from torch.utils.data import ConcatDataset
 #           transform = transforms.Compose([transforms.ToTensor()])
 #           trainset = torchvision.datasets.CIFAR10(root='./data', train=True,
@@ -317,8 +318,7 @@ def num_flat_features(self, x):
 #           #get the mean of each channel            
 #           mean = torch.mean(x, dim=(0,2,3)) #tensor([0.4914, 0.4822, 0.4465])
 #           std = torch.std(x, dim=(0,2,3)) #tensor([0.2470, 0.2435, 0.2616])  
-# 
-#          ```   
+#    
 # 
 # There are many more transforms available, including cropping, centering,
 # rotation, and reflection.