For documentation and usage, see the original repository
Here's how I use this image:
docker run -it --rm \
-e "MONGO_URI=..." \
-e "AWS_ACCESS_KEY_ID=..." \
-e "AWS_SECRET_ACCESS_KEY=..." \
-e "AWS_DEFAULT_REGION=..." \
-e "S3_BUCKET=..." \
-e "MAX_BACKUPS=..." \
karllhughes/mongodump-s3