Add pull request template from CCCL (#550)

Author: kkraus14

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,14 @@
+## Description
+
+<!-- Every PR should have a corresponding issue that describes and motivates the work done in the PR -->
+closes <!-- Link issue here -->
+
+<!-- Provide a standalone description of changes in this PR. -->
+
+<!-- Note: The pull request title will be included in the CHANGELOG. -->
+
+## Checklist
+<!-- TODO: - [ ] I am familiar with the [Contributing Guidelines](). -->
+- [ ] New or existing tests cover these changes.
+- [ ] The documentation is up to date with these changes.
+