*Please* add a meaningful description for your change here.

Once your pull request has been opened and assigned a number, please edit the
URL below, replacing `PULL_REQUEST_NUMBER` with the number of your pull request.

http://apache-beam-website-pull-requests.storage.googleapis.com/PULL_REQUEST_NUMBER/index.html

Finally, it will help us expedite review of your Pull Request if you tag
someone (e.g. @username) to look at it.


Add a pull request template with staged URL
Add a pull request template with staged URL
