fix d2lbook build (#1012)

Co-authored-by: NUbuntu <ubuntu@ip-172-31-12-66.us-west-2.compute.internal>

chapter_computer-vision/kaggle-dog.md

@@ -275,7 +275,7 @@ def evaluate_loss(data_iter, net, devices):
         l = loss(outputs, labels)
         l_sum += l.sum()
         n += labels.numel()
-    return l_sum / n
+    return (l_sum / n).to('cpu')
 ```
 
 ## 定义[**训练函数**]

chapter_deep-learning-computation/deferred-init.md

@@ -120,6 +120,10 @@ net(X)
 [Discussions](https://discuss.d2l.ai/t/1834)
 :end_tab:
 
+:begin_tab:`pytorch`
+[Discussions](https://discuss.d2l.ai/t/1834)
+:end_tab:
+
 :begin_tab:`tensorflow`
 [Discussions](https://discuss.d2l.ai/t/1833)
 :end_tab:

chapter_natural-language-processing-pretraining/subword-embedding.md

@@ -144,3 +144,7 @@ print(segment_BPE(tokens, symbols))
 :begin_tab:`mxnet`
 [Discussions](https://discuss.d2l.ai/t/386)
 :end_tab:
+
+:begin_tab:`pytorch`
+[Discussions](https://discuss.d2l.ai/t/386)
+:end_tab:
\ No newline at end of file