Update PULL_REQUEST_TEMPLATE.md

Author: dbader

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,10 @@
+**Where to put new files:**
+
+- New files should go into a top-level subfolder, named after the article slug. For example: `my-awesome-article`
+
 **How to merge your changes:** 
 
-1. [Make sure the CI code style tests all pass.](https://github.com/realpython/materials/blob/master/README.md)
+1. [Make sure the CI code style tests all pass (+ run the automatic code formatter if necessary).](https://github.com/realpython/materials/blob/master/README.md)
 2. Find an RP Team member on Slack and ask them to review & approve your PR.
 3. Once the PR has one positive ("approved") review, GitHub lets you merge the PR.
 4. 🎉