[MNT] modify pull request template

.github/PULL_REQUEST_TEMPLATE.md

@@ -4,6 +4,8 @@
 <!-- Replace this with a description of the change. -->
 
 ## How has his PR been tested?
+Please cover your changes with tests and attached the screenshots of tests results (if appropriate).
+
 <!---  Put an `x` in the boxes as follows. --->
 - [ ] Please pass the test by running `pytest tests/test_workflow` under upper directory of learnware.
 - [ ] If you add new features, please test new features on your own test scirpt.
@@ -11,5 +13,5 @@
 ## Types of changes
 <!---  Put an `x` in the boxes as follows. --->
 - [ ] This PR fixes bugs
-- [ ] This PR add new features
-- [ ] This PR update documentations or fixes typo
+- [ ] This PR adds new features
+- [ ] This PR updates documentations or fixes typo