docs: Updated Recommending TV Content lesson to support card customization.

<div id="tb">

  <h2>This lesson teaches you to</h2>

  <ol>

    <li><a href="#best-practices">Best Practices for Recommendations</a></li>

    <li><a href="#service">Create a Recommendations Service</a></li>

    <li><a href="#build">Build Recommendations</a></li>

    <li><a href="#run-service">Run Recommendations Service</a></li>

  Leanback sample app</a>.

</p>

<h2 id="best-practices">Best Practices for Recommendations</h2>

<p>Recommendations help users quickly find the content and apps they enjoy. Creating

recommendations that are high-quality and relevant to users is an important factor in creating a

great user experience with your TV app. For this reason, you should carefully consider what

recommendations you present to the user and manage them closely.</p>

<h3 id="types">Types of Recommendations</h3>

<p>When you create recommendations, you should link users back to incomplete viewing activities or

suggest activities that extend that to related content. Here are some specific type of

recommendations you should consider:</p>

<ul>

<li><strong>Continuation content</strong> recommendations for the next episode for users to resume

watching a series.</li>

<li><strong>New content</strong> recommendations, such as for a new first-run episode, if the user

finished watching another series.

<li><strong>Related content</strong> recommendations based on the users historic viewing behavior.

</ul>

<p>For more information on how to design recommendation cards for the best user experience, see

<a href="https://www.google.com/design/spec-tv/system-overview/recommendation-row.html#recommendation-row-types-of-recommendations"

class="external-link">Recommendation Row</a> in the Android TV Design Spec.</p>

<h3 id="refreshing">Refreshing Recommendations</h3>

<p>When refreshing recommendations, don't just remove and repost them, because doing so causes

the recommendations to appear at the end of the recommendations row. Once a content item, such as a

movie, has been played, <a href="{@docRoot}guide/topics/ui/notifiers/notifications.html#Removing">

remove it</a> from the recommendations.</p>

<h3 id="customization">Customizing Recommendations</h3>

<p>You can customize recommendation cards to convey branding information, by setting user interface

elements such as the card's foreground and background image, color, app icon, title, and subtitle.

To learn more, see

<a href="https://www.google.com/design/spec-tv/system-overview/recommendation-row.html#recommendation-row-card-customization"

class="external-link">Recommendation Row</a> in the Android TV Design Spec.</p>

<h2 id="service">Create a Recommendations Service</h2>

        TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);

        stackBuilder.addParentStack(DetailsActivity.class);

        stackBuilder.addNextIntent(detailsIntent);

        // Ensure a unique PendingIntents, otherwise all recommendations end up with the same

        // PendingIntent

        // Ensure a unique PendingIntents, otherwise all

        // recommendations end up with the same PendingIntent

        detailsIntent.setAction(Long.toString(movie.getId()));

        PendingIntent intent = stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);

</manifest>

</pre>

<h3 id="refreshing">Refreshing Recommendations</h3>

<p>Base your recommendations on user behavior and data such as play lists, wish lists, and associated

content. When refreshing recommendations, don't just remove and repost them, because doing so causes

the recommendations to appear at the end of the recommendations row. Once a content item, such as a

movie, has been played, <a href="{@docRoot}guide/topics/ui/notifiers/notifications.html#Removing">

remove it</a> from the recommendations.</p>

<p>The order of an app's recommendations is preserved according to the order in which the app

provides them. The framework interleaves app recommendations based on recommendation quality,

as measured by user behavior. Better recommendations make an app's recommendations more likely

to appear near the front of the list.</p>

<h2 id="build">Build Recommendations</h2>

<p>