Add BERT pretraining tutorial to navigation bar. (#190)

docs/_data/navigation.yml

@@ -48,6 +48,8 @@ lnav:
         url: /tutorials/cifar-10/
       - title: "Megatron-LM GPT2"
         url: /tutorials/megatron/
+      - title: "BERT Pre-training"
+        url: /tutorials/bert-pretraining/
       - title: "1-Cycle Schedule"
         url: /tutorials/1Cycle/
       - title: "Learning Rate Range Test"

docs/_tutorials/bert-pretraining.md

 ---
-title: "Pre-training Bing BERT"
+title: "BERT Pre-training"
 excerpt: ""
 ---