[FIX] use bids uri for qmri derivatives

[Remi-Gau]

fixes #312

@sappelhoff does that make sense as a way to refer to source data in the derivatives using bids uri?

[effigies]

I could swear we had a conversation where we dropped the file:// for relative paths. That's not a universal interpretation of file:///

[effigies]

Oh, I see. That predates the BIDS URI discussion altogether. I would still use plain relative paths. Note in Examples we use relative paths (no file://), absolute paths (with file:///) and external URIs.

[sappelhoff]

mh then we have two ways of specifying relative paths in the spec, should we clarify that?

[Remi-Gau]

mh then we have two ways of specifying relative paths in the spec, should we clarify that?

yes please. 😝