Missing license.txt suggest CC-by-SA #92
Description
It's unclear what license the assets in this repository fall under, specifically of concern are the diagrams and fritzing in this folder: https://github.com/microbit-foundation/dev-docs/tree/master/hardware/assets
These images are widely republished across the internet and it would be good to add an explicit copyleft license such as creative commons share-alike w/ attribution: https://creativecommons.org/licenses/by-sa/4.0/