Update pull request template (helm#4087)

* Wrap general directions into an HTML comment so they are
  not visible in the PR if the user doesn't delete them
* Add template for information a user is supposed to provide
  in order to avoid getting empty descriptions
* Add note on CircleCI

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,4 @@
-*****************************************************************************************
-
+<!--
 Thank you for contributing to kubernetes/charts. Before you submit this PR we'd like to
 make sure you are aware of our technical requirements and best practices:
 
@@ -14,8 +13,20 @@ our review guidelines:
 Following our best practices right from the start will accelerate the review process and
 help get your PR merged quicker.
 
-When updates to your PR are requested, please add new commits and do not squash the 
-history. This will make it easier to identify new changes. The PR will be squashed 
+When updates to your PR are requested, please add new commits and do not squash the
+history. This will make it easier to identify new changes. The PR will be squashed
 anyways when it is merged. Thanks.
 
-*****************************************************************************************
+For fast feedback, please @-mention maintainers that are listed in the Chart.yaml file.
+
+Please make sure you test your changes before you push them. Once pushed, a CircleCI
+will run across your changes and do some initial checks and linting. These checks run
+very quickly. Please check the results. We would like these checks to pass before we
+even continue reviewing your changes.
+-->
+
+**What this PR does / why we need it**:
+
+**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
+
+**Special notes for your reviewer**: