There are two methods we can invoke using RouterModule in order to register routes.
In case we declare the top-level routes of our application, we need to use RouterModule.forRoot. This method will register the top-level routes and return the routing module that should be imported by the root module of the application.
If we want to define routes in a lazy-loaded module and import the module returned by the invocation of the forRoot method, we'll get a runtime error. This is because the forRoot method will return a module with providers, which should be imported only once, by the top-level module. In order to register nested routes in a lazy-loaded module, we will need to use the forChild ...
