Over in https://docs.datasette.io/en/stable/custom_templates.html#serving-static-files, there is the slightly comical example command -

datasette -m metadata.json --static static:static/ --memory

(now, with MORE STATIC!)

It took me a while to sort out all the URLs and paths involved because I wasn't being very clever. But in the interests of simplification and distinction, I might suggest something like

datasette -m metadata.json --static loc:static-files/ --memory

I will submit a PR for your consideration.