An example of how to use readthedocs with sphinx-multiproject! No guarantee this is optimal, this was just my playground to get things working.
Note: you need a separate readthedocs project for each package.
Ensure that you specify the PROJECT environmental variable with the name of the desired package to build.
If desired, you can add one project as a subproject of another.
For example, I set project1 as a subproject of project2.
Therefore, project1 is available at both testingoutthedpocs.readthedocs.io and docs-test-project2.readthedocs.io/projects/package1/.