Update PULL_REQUEST_TEMPLATE (#380)

Fixed some typos that were annoying me :)

PULL_REQUEST_TEMPLATE

@@ -1,13 +1,16 @@
-**Decription**
+# Description
 
-**Submitter checklist**
+See [JENKINS-XXXXX](https://issues.jenkins-ci.org/browse/JENKINS-XXXXX).
+
+# Submitter checklist
+- [ ] Link to JIRA ticket in description, if appropriate.
 - [ ] Change is code complete and matches issue description
 - [ ] Apppropriate unit or acceptance tests or explaination to why this change has no tests
 - [ ] Reviewer's manual test instructions provided in PR description. See Reviewer's first task below.
 
-**Reviewer checklist**
+# Reviewer checklist
 - [ ] Run the changes and verified the change matches the issue description
 - [ ] Reviewed the code
 - [ ] Verified that the appropriate tests have been written or valid explaination given
 
-@reviewbybees 
+@jenkinsci/code-reviewers @reviewbybees