New comment by sgn on void-packages repository

https://github.com/void-linux/void-packages/pull/21272#issuecomment-621683342

Comment:
> I've seen examples of "sed"ed License files from the source.
> Just a FYI that those might be one of the corner cases.

Yes, it's one common case, I've made some LICENSE like that.
We could put that `sed` into `post_patch`.