misc: update pull_request_template

Having too many checklist items are not effective. Combine some of them
and omit those we automatically enforce using github merge policy.

.github/pull_request_template.md

@@ -1,22 +1,15 @@
 ## Pull Request Description
 
-<!--
-Insert description of the work in this merge request (above this comment),
-particularly focused on _why_ the work is necessary, not _what_ you did.
--->
-
-<!-- AUTHOR: After creating this merge request, check off each of the following items as you complete them. -->
-
-## Expected Impact
 
 ## Author Checklist
-* [ ] Reference appropriate issues (with "Fixes" or "See" as appropriate)
-* [ ] Remove xfail from the test suite when fixing a test
-* [ ] Commits are self-contained and do not do two things at once
-* [ ] Commit message is of the form: `module: short description` and follows [good practice](https://chris.beams.io/posts/git-commit/)
-* [ ] Passes whitespace checkers
-* [ ] Passes warning tests
-* [ ] Passes all tests
-* [ ] Add comments such that someone without knowledge of the code could understand
-* [ ] You or your company has a signed contributor's agreement on file with Argonne
-* [ ] For non-Argonne authors, request an explicit comment from your companies PR approval manager
+* [ ] **Provide Description** 
+      Particularly focus on _why_, not _what_. Reference background, issues, test failures, xfail entries, etc.
+* [ ] **Commits Follow Good Practice**
+      Commits are self-contained and do not do two things at once. 
+      Commit message is of the form: `module: short description` 
+      Commit message explains what's in the commit.
+* [ ] **Passes All Tests**
+      Whitespace checker. Warnings test. Additional tests via comments.
+* [ ] **Contribution Agreement**
+      For non-Argonne authors, check [contribution agreement](http://www.mpich.org/documentation/contributor-docs/). 
+      If necessary, request an explicit comment from your companies PR approval manager.