Create pull request template (#529)

Author: Rachael-E

.github/pull_request_template.md

@@ -0,0 +1,13 @@
+<!-- Give the PR a meaningful title that makes for a concise description of the content within the PR. For example, the title of a PR for a new sample should be "New sample: xxx" or for a bug fix, "Patch: fix (description of bug) in sample x". -->
+
+<!-- If you are merging a sample for the current release, ensure the target branch is `master`. If merging a sample for the next release, ensure the target branch is `dev`. -->
+
+### Description
+
+<!-- Give a brief summary description (one or two sentences) of the work done within the PR, and also write any particular points on which you'd like specific feedback/advice on. Ensure to both request a review and also assign that reviewee, as well as tag them in this PR description. -->
+
+Checklist:
+- [ ] Set target branch to master (current release) or dev (next release)
+- [ ] Request a reviewer
+- [ ] Assign a reviewer
+- [ ] Tag reviewer in comment