Usage:

docker build -t backupinator .

docker run \
    -v /path/to/folder1:/in/folder1:ro \
    -v /path/to/folder2:/in/folder2:ro \
    -v /path/to/output:/output \
    -v /path/to/key1.pub:/keys/key1.pub:ro \
    -v /path/to/key2.pub:/keys/key2.pub:ro \
    backupinator