Add flake.nix packaging

.gitignore

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+result*

doc/.gitignore

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+sshping.8
+sshping.8.gz

flake.nix

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+{
+  description = "Measure character-echo latency and bandwidth for an interactive ssh session";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  outputs =
+    { self, nixpkgs }:
+    let
+      system = "x86_64-linux";
+      pkgs = import nixpkgs { inherit system; };
+    in
+    {
+      formatter.${system} = pkgs.nixfmt-tree;
+
+      packages.${system} = {
+        default = pkgs.stdenv.mkDerivation {
+          pname = "sshping";
+          version = "master";
+
+          outputs = [ "out" "man" ];
+
+          src = self;
+
+          buildInputs = with pkgs; [ libssh perl ];
+
+          buildPhase = ''
+            make bin/sshping
+            make doc/sshping.8.gz
+          '';
+
+          installPhase = ''
+            install -Dm755 bin/sshping $out/bin/sshping
+            install -Dm644 doc/sshping.8.gz $man/share/man/man8/sshping.8.gz
+          '';
+
+          meta = {
+            homepage = "https://github.com/spook/sshping";
+            description = "Measure character-echo latency and bandwidth for an interactive ssh session";
+            license = pkgs.lib.licenses.mit;
+            platforms = pkgs.lib.platforms.unix;
+            maintainers = with pkgs.lib.maintainers; [ spook ];
+            outputsToInstall = [ "out" "man" ];
+            mainProgram = "sshping";
+          };
+        };
+      };
+    };
+}