feat: install git-entr script

The script lists all files in the git repository that are not ignored, and runs a given command on change using entr.

users/buffet/git-entr.nix

@@ -0,0 +1,15 @@
+{pkgs, ...}: {
+  home-manager.users.buffet = {
+    home.packages = [
+      (pkgs.writeScriptBin "git-entr" ''
+          #!/bin/sh
+
+          echo "looping entr. press ctrl-c twice to exit"
+
+          while sleep 1; do
+              git ls-files -cdmo --exclude-standard | entr -d "$@"
+          done
+      '')
+    ];
+  };
+}