Update PR template to include doc updates (#43)

Author: PiotrWodecki

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,21 @@
+## Description
+
+Describe your changes.
+
+## Motivation and Context
+
+Why is this change required? What problem does it solve? If it fixes an open
+issue, please link to the issue here.
+
+## Documentation impact
+
+- [ ] Documentation update required
+- [ ] Documentation updated [in another PR](_)
+- [ ] No documentation update required
+
+## Types of changes
+
+- [ ] Bug fix (non-breaking change which fixes an issue)
+- [ ] New feature (non-breaking change which adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to
+      not work as expected)