License-File in sdist metadata

[mtelka]

There is no License-File entry in the sdist metadata. Since this project uses license file at non-standard location (docs/license.rst) it would be great if the license file path is recorded in the metadata to make it easier to find the license. Thank you.

Please note that I do NOT need new (either .post or regular) release just with this single issue fixed. IOW, it is not a blocker for me.