[Extensions Docs] Update SettingsOverrides to indicate Mac availability

chrome/common/extensions/docs/templates/articles/settings_override.html

 <h1>Settings Overrides</h1>
 
 <p>
 Settings overrides are a way for extensions to override selected Chrome settings.
-The API is available only on Windows.
+The API is available on Windows in all current versions of Chrome and is
+available on Mac in Chrome 56 and later.
 </p>
 
 <h2 id="others">Homepage, Search Provider, and Startup Pages</h2>
 <p>
 Here is an example how <a href="#homepage">homepage</a>, <a
 href="#search_provider">search provider</a> and <a href="#startup_pages">startup
 pages</a> can be modified in the <a href="manifest">extension
 manifest</a>. Web sites used in the settings API must be
 <a href="https://support.google.com/webmasters/answer/35179">verified</a> (via
 Webmaster Tools) as being associated with that item in the Chrome Web Store.
@@ skipping 57 matching lines @@
   </li>
 </ul>
 
 <h2 id="reference">Reference</h2>
 <p>
 An extension can override one or more of the following properties in the
 manifest:
 </p>
 {{+partials.manifest_type
    type:apis.extensions.manifestTypes.byName.ChromeSettingsOverrides /}}