Mention Documentation in PR Template (#2570)

.github/pull_request_template.md

@@ -4,4 +4,8 @@ _Describe the purpose of and changes within this Pull Request._
 
 ## Testing
 
-_Do any existing tests cover this change? Are new tests needed?_
+_Do any existing tests cover this change? Are new tests needed?_
+
+## Documentation
+
+_Is there any documentation impact for this change?_