Clarify status of this project

[nikola-da]

This project helped us quite a lot in setting up our Nix+Haskell ecosystem. However, it seems to be stale, as there are no updates to definitions in the last 4 months, even tho there have been many new stackage releases. Please clarify the future of this project, when should we expect any new updates, or should we abandon it.

[dredozubov]

We don't use newer snapshots in our in-house projects right now, so there was little motivation to update it. Feel free to generate new snapshots as stated in the readme file https://github.com/typeable/nixpkgs-stackage/blob/master/README.md and open a PR to this repo