Nix flake (#758)

* Added Flake for nix

* Removed Cargo lock from ignore

As it's now reccomended by rust team to keep it in repo as well as nix
needs it fetch dependacies for nix run

* Added Nix Compatbilty for package

I forgot to add it that's why this commit is here.

* Made flake minimal

shell.nix

@@ -0,0 +1,13 @@
+(import
+  (
+    let
+      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+      nodeName = lock.nodes.root.inputs.flake-compat;
+    in
+    fetchTarball {
+      url = lock.nodes.${nodeName}.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.${nodeName}.locked.rev}.tar.gz";
+      sha256 = lock.nodes.${nodeName}.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).shellNix