Settings Override API: update documentation.

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.
 </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
@@ skipping 28 matching lines @@
    },
    "default_locale": "de",
    ...
 }</pre>
 
 <p class="note">
 <b>Note:</b> Settings overrides for <code>homepage</code>,
 <code>search_provider</code>, and <code>startup_pages</code> are only enabled
 in the Chrome Dev release.</p>
 
+<h2 id="customizing">Customizing values</h2>
+<p>Values in the manifest can be customized in the following ways:</p>
+<ul>
+  <li>
+  All values of the <code>search_provider</code>, <code>homepage</code> and
+  <code>startup_pages</code> properties can be localized using the
+  $(ref:i18n chrome.i18n API).
+  </li>
+  <li>
+  For <a href="http://developer.chrome.com/extensions/external_extensions">external extensions</a>,
+  the <code>search_provider</code>, <code>homepage</code> and
+  <code>startup_pages</code> URL values can be parametrized using a registry key.
+  A new registry entry should be created next to the "update_url" key (see
+  instructions <a href="http://developer.chrome.com/extensions/external_extensions#registry">here</a>).
+  The value name is "install_parameter", the value data is an arbitrary string:
+  <pre>{
+    "update_url": "https://clients2.google.com/service/update2/crx",
+    "install_parameter": "Value"
+  }</pre>
+  All occurrences of the substring "__PARAM__" in the manifest URLs will be
+  substituted with the "install_parameter" value. If “install_parameter” is
+  absent, occurrences of "__PARAM__" are removed. Note that "__PARAM__" cannot
+  be part of the hostname. It needs to occur after the first '/' in the URL.
+  </li>
+</ul>
+
 <h2 id="reference">Reference</h2>
 <p>
 An extension can override one or more of the following properties in the
 manifest:
 </p>
 
 <ul>
 {{#f:apis.manifestTypes.byName.ChromeSettingsOverrides.properties}}
   <li>
   <p id="{{f.name}}"><b><code>{{f.name}}</code> ({{+partials.variable_type type:f/}})</b></p>
   <p>{{f.description}}</p>
   {{?f.properties}}
     <table>
     <tr><th>Type</th><th>Attribute</th><th>Description</th></tr>
     {{+partials.type_item
        title:f.strings.properties
        display_name:display_name
        items:f.properties
        item_partial:(partials.parameter_full hideParamTOC:true)/}}
     </table>
   {{/}}
 {{/}}
 </ul>