Install syncthing

- Home-manager's syncthing only allows imperative config; as I'd like to use it
  I'll need to configure imperatively too
- I use syncthing to sync up my private directory (i.e. password databases etc.)
diff --git a/modules/syncthing.nix b/modules/syncthing.nix
new file mode 100644
index 0000000..af0f2be
--- /dev/null
+++ b/modules/syncthing.nix
@@ -0,0 +1,5 @@
+{username, ...}: {
+  home.services.syncthing.enable = true;
+
+  config.environment.persistence."/nix/persist".users.${username}.directories = ["Sync" ".config/syncthing"];
+}