add more info to 'ValueError' exception message (#502)
add more info to 'ValueError' exception message (#502)

* add more info to exception message

* Update thinc/backends/__init__.py

Co-authored-by: Sofie Van Landeghem <4da0510fc9ac6504702ef47a8b3fc3d8fc7be21b@users.noreply.github.com>

Co-authored-by: Sofie Van Landeghem <4da0510fc9ac6504702ef47a8b3fc3d8fc7be21b@users.noreply.github.com>
spacy-io/thinc,spacy-io/thinc,spacy-io/thinc,explosion/thinc,explosion/thinc,explosion/thinc,explosion/thinc