Include LICENSE in the crate

[sayanchowdhury]

I'm packaging netmap_sys for Fedora. I found that the LICENSE was not included in the crate. It would be good to have the LICENSE in the crate, so that it would be distributed along with the RPM package.

[igor-raits]

I think it meant to be LICENSE here.

[sayanchowdhury]

@ignatenkobrain thanks! my mistake it should be LICENSE.