add instructions for pr template usage

Author: WilliamHYZhang

docs/add_dataset.md

@@ -556,7 +556,11 @@ for more information.
 
 ### 6. Send for review!
 
-Send the pull request for review.
+Send the pull request for review. When creating the pull request, please use the
+`add_dataset` template, which provides a guide and a checklist for adding a
+dataset to TFDS. To use the template, simply add `?template=add_dataset.md` at
+the end of the link when creating the pull request. For example, 
+`https://github.com/tensorflow/datasets/compare/master...<username>:<branch>?template=add_dataset.md`
 
 
 ## Define the dataset outside TFDS.