Create pull_request_template.md (#316)

* Create pull_request_template.md

* More accurate wording.

* Update pull_request_template.md

.github/pull_request_template.md

@@ -0,0 +1,11 @@
+Before opening your pull request, please respond to the following prompts.
+
+#### Is this resolving a feature or a bug?
+
+_NB: We DO NOT accept typo fixes. Generally, we do not accept edits to comments (starting with `//`) or minor grammatical and technical edits more generally, but do accept substanative fixes and improvements to the content of documentation comments (`///`) and README files._
+
+#### Are there existing issue(s) that this PR would close?
+
+#### If this PR is not minimal (it could be split into multiple PRs), please explain why the issues are best resolved together. 
+
+#### Describe your changes.