Merge pull request mozilla#18940 from Snuffleupagus/bug-report-PDF-placeholder

Try to discourage "unrelated" information under `Attach (recommended) or Link to PDF file` in the bug report template (PR 18535 follow-up)

Author: timvandermeij

.github/ISSUE_TEMPLATE/bug.yml

@@ -6,6 +6,7 @@ body:
     attributes:
       label: Attach (recommended) or Link to PDF file
       description: Without this information the issue may be closed without comment
+      placeholder: Please place only the PDF file in this field
     validations:
       required: true