refs #3222: add PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,18 @@
+Subject: <short purpose of this pull request>
+
+### Feature or Bugfix
+<!-- please choose -->
+- Feature
+- Bugfix
+
+### Purpose
+- <long purpose of this pull request>
+- <Environment if this PR depends on>
+
+### Detail
+- <feature1 or bug1>
+- <feature2 or bug2>
+
+### Relates
+- <URL or Ticket>
+