This file is here for those who are building/exploring OMPI in its source code form, most likely through a developer's tree (i.e., a Git clone).
Please see the content of this file in its new location: https://docs.open-mpi.org/en/main/developers/
Additionally, see https://docs.open-mpi.org/en/main/developers/prerequisites.html#sphinx-and-therefore-python if you want to edit and build the documentation locally.