Add issue link for the experimental CLI (#17659)

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,8 @@
 blank_issues_enabled: true
 contact_links:
+  - name: Issue with experimental CLI
+    url: https://github.com/prettier/prettier-cli/issues
+    about: The experimental CLI currently lives in a separate repo, open an issue there instead.
   - name: 🤔 Support question
     url: https://stackoverflow.com/questions/ask?tags=prettier
     about: Issues are dedicated to development purposes. If you have questions, please use Stack Overflow.