* Update documentation and CI configurations to work around OpenBLAS OpenMP thrashing issue. * Update out-of-date link. * Clarify the situation on Ubuntu and Debian. * Clarify about pthread compilation. * Add a bit about the OpenMP variant. * Make the verbiage consistent everywhere. * Try to see if the fix works on macOS too. * Homebrew packages OpenBLAS 0.3.28, so no workaround is needed.