I'm trying to understand this sentence. I have set the "which" in bold:
If you start a container which creates a new volume, as above, and the container has files or directories in the directory to be mounted (such as /app/ above), the directory’s contents are copied into the volume.
Why doesn't this sentence use a comma before "which" (i.e. "[...] container, which creates [...]")?
When should I use a comma before "which", and what's the difference?