Sphinx 8: WARNING: document isn't included in any toctree [toc.not_included]

[amotl]

Problem

Recent RTD builds started failing out of the blue?

checking consistency... /home/docs/checkouts/readthedocs.org/user_builds/cratedb-toolkit/checkouts/584/doc/readme.md:
WARNING: document isn't included in any toctree [toc.not_included]

-- https://app.readthedocs.org/projects/lorrystream/builds/30797418/#299483796--38

References

• [DOCS] Sphinx 8: WARNING: document isn't included in any toctree [toc.not_included] crate/cratedb-toolkit#587
• Regression with Sphinx 8 and symlinks: document isn't included in any toctree [toc.not_included] sphinx-doc/sphinx#14520