fix(docs-infra): Images must have alternate text

Author: timdeschryver

projects/ngrx.io/content/marketing/index.html

@@ -1,5 +1,5 @@
 <header>
-  <img src="assets/images/badge.svg"/>
+  <img src="assets/images/badge.svg" alt="ngrx-logo" title="ngrx-logo"/>
   <div class="title no-toc">NgRx</div>
   <div class="subtitle no-toc">Reactive State for Angular</div>
   <a class="cta mat-raised-button mat-accent" href="guide/store">