doc: Add link to video + minor update on Index page.

Author: alexyakunin

README.md

@@ -45,6 +45,9 @@ which also serves its API. The application includes:
 * "Authentication" – a GitHub authentication sample with Google-style real-time 
   session tracking, "Kick", and "Sign-out everywhere" actions.
 
+> Check out a [7-min. video walk-through](https://www.youtube.com/watch?v=nBJo9Y2TvEo) 
+> for this sample - the animations below show just some of its features.
+
 ![](docs/img/Samples-Blazor.gif)
 
 Note that "Composition" sample shown in a separate window in the bottom-right corner

src/Blazor/Client/Pages/Index.razor

@@ -1,11 +1,14 @@
 @page "/"
 
-<div class="jumbotron">
+<div class="jumbotron" xmlns="http://www.w3.org/1999/html">
     <h1 class="display-4">Welcome!</h1>
-    <p class="lead">This is Stl.Fusion Blazor sample.</p>
-    <p><BlazorModeSwitch /></p>
-    <p class="lead">Please share your feedback once you're done with it!</p>
+    <p class="lead">This is Fusion+Blazor sample - the most advanced one we have.</p>
+    <p>
+        Choose the mode to use:<br/>
+        <BlazorModeSwitch/>
+    </p>
     <hr class="my-4">
+    <p class="lead">Please share your feedback once you're done playing with it!</p>
     <p class="lead">
         <a class="btn btn-primary btn-lg" href="https://forms.gle/TpGkmTZttukhDMRB6" role="button">Share your feedback</a>
     </p>