Add pull request template.

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,27 @@
+## Description
+
+<!-- Describe your changes. -->
+
+## Motivation and context
+
+<!--- Why is this change required? What problem does it solve? -->
+
+<!-- Replace ??? with the issue number that this pull request resolves. -->
+Resolves #???
+
+## How has this been tested?
+
+<!--- Please describe how you tested your changes. -->
+
+## Change log
+
+<!-- Propose a change log entry. -->
+```
+
+```
+
+## Checklist:
+
+- [ ] I have reviewed the [**Contributor Guidelines**](https://github.com/glotzerlab/row/blob/trunk/doc/src/developers/contributing.md).
+- [ ] I agree with the terms of the [**Row Contributor Agreement**](https://github.com/glotzerlab/row/blob/trunk/ContributorAgreement.md).
+- [ ] My name is on the list of contributors (`doc/src/contributors.md`) in the pull request source branch.

DESIGN.md

@@ -294,7 +294,6 @@ status may take a long time, so it should display a progress bar.
   without applying the additional submission filters.
 - **workspace**: The location on the file system that contains **directories**.
 
-# TODO: Pull request template
 # TODO: Issue templates?
 # TODO: Dependabot configuration
 # TODO: readthedocs builds