Redirect visitors to external schema and workflow documentation

[eecavanna]

This is related to ADR-0010 (draft):

• https://github.com/microbiomedata/issues/blob/0010-doc-building/decisions/0010-documentation-setup.md
• TODO: Update this URL once the ADR has been merged into the issues repository.

Here's a Sphinx extension that people can use to implement redirects: https://pypi.org/project/sphinx-reredirects/