Use a volume or copy my artefacts into docker image
To copy into the image or to mount volumes--my advice:

if the files will change infrequently, then copy them into the image, with the understanding that if they need to be modified, you will need to rebuild the image.
if you need to frequently change the files, or store some kind of state about the files (and re-use them with future container instances of the image), then mount them as volumes.