Add PR template (#74)

Author: Chris Cho

.github/pull_request_template.md

@@ -0,0 +1,19 @@
+## Pull Request Info
+
+### Issue JIRA link:
+https://jira.mongodb.org/browse/DOCSP-NNNNN
+
+### Snooty build log:
+**Paste your workerpool job link here**
+
+### Docs staging link (requires sign-in on MongoDB Corp SSO):
+https://docs-mongodborg-staging.corp.mongodb.com/NNNNNNN/spark/docsworker-xlarge/NNNNNNNNNNN/
+
+### Self-Review Checklist
+
+- [ ] Is this free of any warnings or errors in the RST?
+- [ ] Did you run a spell-check?
+- [ ] Did you run a grammar-check?
+- [ ] Does it render on staging correctly?
+- [ ] Are all the links working?
+- [ ] Are the staging and workerpool job links in the PR description updated?