Switch directories and volume examples in accessories.md

[jakeprem]

This better matches how these are being used with Docker. The directories setting is passing in a directory from a path, while the volumes setting will create a docker volume with the given name.

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The Volumes section also states:
"Any other volumes to mount, in addition to the files and directories. They are not created or copied before mounting:"

I wonder if this should also be updated to clarify that it will create the Docker volume if it doesn't exist.

Tat's the behavior I observed anyway. I switched from a directory mount to a volume for my database accessory's data and the Docker volume was created automatically.