Add ecryptfs for file encryption
diff --git a/modules/ecryptfs.nix b/modules/ecryptfs.nix
new file mode 100644
index 0000000..9210ca0
--- /dev/null
+++ b/modules/ecryptfs.nix
@@ -0,0 +1,6 @@
+{ pkgs, ... }: {
+  environment.systemPackages = with pkgs; [
+    ecryptfs
+    ecryptfs-helper
+  ];
+}