The contrib directory contains packages that do not belong in the core containerd packages but still contribute to overall containerd usability.
Package such as Apparmor or Selinux are placed in contrib because they are platform dependent and often require higher level tools and profiles to work.
Packaging and other built tools can be added to contrib to aid in packaging containerd for various distributions.
Code in the contrib directory may or may not have been tested in the normal test pipeline for core components.