Update metadata.rst
Update metadata.rst

Added the undocumented containerEngine
nextflow-io/nextflow,nextflow-io/nextflow,robsyme/nextflow,heuermh/nextflow,heuermh/nextflow,robsyme/nextflow,heuermh/nextflow,robsyme/nextflow,nextflow-io/nextflow,robsyme/nextflow,heuermh/nextflow,nextflow-io/nextflow,heuermh/nextflow,robsyme/nextflow,nextflow-io/nextflow