Add Unified Embedding tutorial.

PiperOrigin-RevId: 812244566

Author: TensorFlow Recommenders Authors

assets/embedding_baseline.png

@@ -34,6 +34,8 @@ toc:
   path: /recommenders/examples/multitask
 - title: "Cross networks"
   path: /recommenders/examples/dcn
+- title: "Unified embedding"
+  path: /recommenders/examples/uet
 - title: "Efficient serving"
   path: /recommenders/examples/efficient_serving
 - title: "Listwise ranking"