Proposal for PR template (#542)

* Create PULL_REQUEST_TEMPLATE.md

* Add checkbox for "adds tests"

* Update template

* Update CHANGELOG.md

* Update PULL_REQUEST_TEMPLATE.md

* Update PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,17 @@
+**Thanks for contributing to Prefect!**
+
+Please describe your work and make sure your PR:
+
+- [ ] adds new tests (if appropriate)
+- [ ] updates `CHANGELOG.md` (if appropriate)
+- [ ] updates docstrings for any new functions or function arguments, including `docs/outline.toml` for API reference docs (if appropriate)
+
+
+
+## What does this PR change?
+
+
+
+## Why is this PR important?
+
+

CHANGELOG.md

@@ -14,6 +14,7 @@
 - Add hooks to `FlowRunner.initialize_run()` for manipulating task states and contexts - [#548](https://github.com/PrefectHQ/prefect/pull/548)
 - Improve state-loading strategy for Prefect Cloud - [#555](https://github.com/PrefectHQ/prefect/issues/555)
 - Introduce `on_failure` kwarg to Tasks and Flows for user-friendly failure callbacks - [#551](https://github.com/PrefectHQ/prefect/issues/551)
+- Add PR template - [#542](https://github.com/PrefectHQ/prefect/pull/542)
 
 ### Fixes