Nix support & automated update (#130)

* Add a nix flake

* Update flake deps and nix package's version nightly

* nix-flake: Update vendorSha256 on each push

An extra commit will be pushed only if needed

* Move flake.* into root directory

Update flake.lock

* nix-flake: Support more systems, commit hash as version

* Don't automatically update flake.lock

nix/prefetcher.nix

@@ -0,0 +1,11 @@
+{
+  sha256,
+  pkgs ? import <nixpkgs> {},
+}:
+pkgs.callPackage (import ./.) {
+  buildGoModule = pkgs.buildGo118Module;
+  vendorSha256 = sha256;
+}
+// {
+  outputHash = sha256;
+}