nix develop and nix build work

Author: peterbecich

README.md

@@ -22,6 +22,12 @@ If you have the [Nix package manager](https://nixos.org/) installed, the easiest
     $ cabal v2-run -- hackage-server run --static-dir=datafiles/ --base-uri=http://127.0.0.1:8080
     hackage-server: Ready! Point your browser at http://127.0.0.1:8080
 
+`flake.nix` is provided; it uses [`srid/haskell-flake`](https://github.com/srid/haskell-flake).
+
+If you have [direnv](https://direnv.net/), `direnv allow` will load this `nix develop` shell automatically.
+
+`nix build` will build a `hackage-server` executable in `result/`. The Hackage dependencies are provided by the inputs specified in `flake.nix`.
+
 ### Manually
 
 You can also install dependencies manually via your operating system's package