add separator after introduction to tutorial ends (#89)

tutorial/tutorial_1_node_lifecycle.cpp

@@ -20,6 +20,8 @@
 /// The `logos-libp2p-module` wraps nim-libp2p's C bindings into a C++ class
 /// called `Libp2pModuleImpl` that you can embed directly into your application.
 ///
+/// -----------
+
 /// ## Step 1: Include the module header and instantiate a node
 ///
 /// Every program starts by including the module's single public header: