artifact metadata

[errordeveloper]

Having some description/docs/URLs embedded with an artifact would be quite useful, as right now the only directly human-readable attribute of an artifact is its name.

It should be possible to e.g. include README files by default. In the presence of VCS, it might be possible to derive e.g. GitHub URL. It should also be possible to override this behaviour with a flag and provide additional metadata.

[errordeveloper]

cc @ipedrazas