Make repository a nix flake

Make git-email.el a nix flake for an easier installation process for
Nix users.  It currently exposes two packages:

- git-email-full -- This includes all the optional libraries
- git-email -- This only includes the core `git-email.el` library

They both get the source from directory from the git repository,
meaning they will get updates as soon as a commit is made.

* default.nix: Add file.
* flake.lock: Add file.
* flake.nix: Add file.

1 files changed, 17 insertions, 0 deletions

diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..176f27e
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,17 @@
+{
+  description = "git-email.el flake";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let pkgs = nixpkgs.legacyPackages.${system};
+      in
+      rec {
+        packages = pkgs.lib.recurseIntoAttrs (pkgs.callPackage ./. {});
+        defaultPackage = packages.git-email-full;
+      });
+}