Add git churn

modules/git-churn.nix

@@ -0,0 +1,23 @@
+{ pkgs, ... }:
+
+{
+  environment.systemPackages = [
+    (pkgs.writeShellApplication {
+      name = "git-churn";
+
+      runtimeInputs = with pkgs; [
+        git
+        coreutils
+        gnugrep
+      ];
+
+      text = ''
+        git log -M -C --name-only --format='format:' "$@" |
+          sort |
+          grep -v '^$' |
+          uniq -c |
+          sort -n
+      '';
+    })
+  ];
+}