Editorial: Add naming and labeling conventions to PR template (#2319)

.github/pull_request_template.md

@@ -2,7 +2,9 @@ Closes #????
 
 Describe Change Here!
 
-<!--- IF EDITORIAL or CHORE, delete the rest of this template -->
+And a few other todo items (delete this section after performing them):
+* [ ] For every spec that this PR edits, please add the appropriate `spec:<spec_name>` label. If you don't have privileges to do this, editors will do it for you.
+* [ ] If the change is [editorial](https://github.com/w3c/aria/blob/main/documentation/process.md#editorial-changes), please add "Editorial:" at the start of your PR name, and delete the "Test, Documentation and Implementation tracking" section below.
 
 # Test, Documentation and Implementation tracking
 Once this PR has been reviewed and has consensus from the working group, tests should be written and issues should be opened on browsers. Add N/A and check when not applicable.