docs: Changed text as requested in Android TV advertising bug, with minor cleanup

<h2 id="advertising">Provide Effective Advertising</h2>

<p>Advertising on Android TV must always be full-screen. Ads must not appear alongside or over

content. The user must be able to dismiss an advertisement with the D-pad controller. Video ads must

be dismissible within 30 seconds of their start time.</p>

<p>For the living room environment, we recommend you use video ads solutions

that are full-screen and dismissable within 30 seconds. Functionality for

advertising on Android TV, such as dismiss buttons and clickthroughs, must be

accessible using the D-pad rather than touch.</p>

<p>Android TV does not provide a web browser. Your ads must not attempt to launch a web browser or

redirect to the Google Play Store.</p>

<p>Android TV does not provide a web browser. Your ads must not attempt to

launch a web browser or redirect to Google Play Store content that is not

approved for Android TV devices.</p>

<p class="note">

  <strong>Note:</strong> You can use the {@link android.webkit.WebView} class for logins to

  services like Google+ and Facebook.

  <strong>Note:</strong> You can use the {@link android.webkit.WebView} class

  for logins to services like Google+ and Facebook.

</p>

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