Processing attachments (update documentation, have GitHub template for it?)

Decide on a workflow (e.g. GitHub-based) how attachments should be added when asked for and update documentation accordingly. See related open issues on concrete examples illustrating the need.

> those forms were for bulk ingestion of attachments. We should delete the FAQ entry since we no longer use this form. We could also add a new Github-based form (similar to PDF corrections) to allow uploading of attachments.

_Originally posted by @mjpost in [#7272](https://github.com/acl-org/acl-anthology/issues/7272#issuecomment-3806762956)_

Need to update
- [x] FAQ: https://aclanthology.org/faq/
- [ ] Wiki page: https://github.com/acl-org/acl-anthology/wiki/Processing-attachments-and-corrections

Potentially introduce
- [ ] a new GitHub template
- [ ] a script to handle attachments or update existing script if necessary

Related, still open issues:
- #7272 user would like to add an attachment to their ACL 2025 publication
- #4161 user would like to add an attachment to their (unnamed) ACL 2023 publication, would even offer a PR
- #1773 stating the Microsoft form mentioned in the FAQ is closed
- #493 (this sounds more like bulk ingestions, and it's from 2019)