title: Why I need to add '/' to routerLink but we do not have '/' in router definination?
body: <p>I am following <a href="https://angular.io/tutorial/toh-pt5" rel="nofollow noreferrer">angular official tutorial</a>. This question confused me, but this tutorial did not explain why so.</p>
  
  <p>When we click a  element, we route to a view/template. You can see, we have '/heroes', why we need to add '/' in here? I removed the '/', then the router cannot work.</p>
  
  <pre><code>template: `
     &lt;h1&gt;{{title}}&lt;/h1&gt;
     &lt;nav&gt;
       &lt;a routerLink="/dashboard"&gt;Dashboard&lt;/a&gt;
       &lt;a routerLink="/heroes"&gt;Heroes&lt;/a&gt;
     &lt;/nav&gt;
     &lt;router-outlet&gt;&lt;/router-outlet&gt;
  </code></pre>
  
  <p>Here is the router definition, but it does not have '/'.</p>
  
  <pre><code>const routes: Routes = [
    { path: '', redirectTo: '/dashboard', pathMatch: 'full' },
    { path: 'dashboard',  component: DashboardComponent },
    { path: 'detail/:id', component: HeroDetailComponent },
    { path: 'heroes',     component: HeroesComponent }
  ];
  </code></pre>