The rpm-ostree-devel package includes the header files for rpm-ostree-libs.
acquired package info from repodata DB: repodata/69e709f4d2852d98f12867a74015d19384fe2727ff670fd70178cdde80b1e77e-primary.sqlite.bz2
The ostree-devel package includes the header files for the ostree library.
The rpm-ostree-libs package includes the shared library for rpm-ostree.