CHANGELOG: add an in-repo changelog file
CHANGELOG: add an in-repo changelog file

This will make releases much simpler. I've back-filled the changelog
with everything since runc 1.0.0 (there's not much point going further
back than that).

Signed-off-by: Aleksa Sarai <b305c9b0212d6145eea67bbffd24e29cb79c759c@cyphar.com>

kolyshkin/runc,opencontainers/runc,opencontainers/runc,kolyshkin/runc,kolyshkin/runc,kolyshkin/runc,opencontainers/runc,opencontainers/runc