Add flake for devShells

This flake adds dev shells for x86 linux and both x86/arm mac
development. Right now it's using a crystal flake I made in my own
github account, but we can move that to crunchy's nixpkgs once we get
that going.

The flake does not provide a build yet for cb, but that should be
possible in the future.

.gitattributes

@@ -0,0 +1,2 @@
+shard.lock linguist-generated
+flake.lock linguist-generated

flake.nix

@@ -0,0 +1,29 @@
+{
+  description = "CrunchyBridge CLI";
+
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    nixpkgs-crystal = {
+      url = "github:will/nixpkgs-crystal";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = { self, nixpkgs, nixpkgs-crystal, flake-utils }:
+    let
+      systems = (builtins.attrNames nixpkgs-crystal.outputs.packages);
+    in
+    flake-utils.lib.eachSystem systems (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        crystal = nixpkgs-crystal.packages.${system}.crystal;
+      in
+      {
+
+        devShells.default = pkgs.mkShell {
+          buildInputs = [ crystal pkgs.libssh2 ];
+        };
+
+      }
+    );
+}