metadata correction issue template: suggest a PR (#3799)

.github/ISSUE_TEMPLATE/01-metadata-correction.yml

@@ -5,6 +5,14 @@ labels: ["correction", "metadata"]
 assignees:
   - anthology-assist
 body:
+  - type: markdown
+    attributes:
+      value: >
+        This form will report paper metadata issues to Anthology staff.
+        Each paper's metadata is stored in an [XML](https://github.com/acl-org/acl-anthology/tree/master/data/xml)
+        record, and is supposed to match what appears in the PDF.
+        If you can, submitting a __pull request__ instead of this form will expedite the process
+        (please include a link to the paper as a comment in the pull request). Thanks!
   - type: checkboxes
     id: paper_metadata_confirmation
     attributes: