ci: Add comment explaining adding labels after creating a PR

.github/workflows/download_translations.yml

@@ -77,6 +77,10 @@ jobs:
             --head l10n_crowdin_translations \
             --base master)
 
+          # This has to be done separately from creating a PR, because
+          # GitHub currently has issues with creating a PR with labels.
+          # Basically creating a PR works, adding labels works, but creating
+          # a PR with labels doesn't ¯\_(ツ)_/¯
           gh pr edit "$pr_url" --add-label T-chore --add-label A-i18n
         env:
           # Use a custom token rather than the automatic GITHUB_TOKEN, as the automatic one doesn't allow created PRs to trigger workflows