Update documentation for "file_system_provider" manifest section.

chrome/common/extensions/docs/templates/intros/fileSystemProvider.html

 <h2 id="manifest">Manifest</h2>
-<p>You must declare the "fileSystemProvider" permission
+<p>You must declare the "fileSystemProvider" permission and section
 in the <a href="manifest">extension manifest</a>
 to use the File System Provider API.
 For example:</p>
 <pre data-filename="manifest.json">
 {
   "name": "My extension",
   ...
-  <b>"permissions": [
+  "permissions": [
     "fileSystemProvider"
-  ]</b>,
+  ],
+  ...
+  "file_system_provider": [
+    "configurable": true,
+    "multiple_mounts": true,
+    "source": "network"
+  ],
   ...
 }
 </pre>
 
+<p class="api_reference">
+The <code>file_system_provider</code> section must be declared as follows:
+{{+partials.manifest_type
+   type:apis.extensions.manifestTypes.byName.FileSystemProviderCapabilities /}}
+</p>
+
 <h2 id="overview">Overview</h2>
 <p>
 File System Provider API allows extensions to support virtual file systems,
 which are available in the file manager on Chrome OS.
 Use cases include decompressing archives and accessing files in a cloud
 service other than Drive.
 </p>
 
 <h2 id="archives">File handlers</h2>
 <p>
@@ skipping 18 matching lines @@
 <a href="#method-unmount"> unmount</a> method.
 </p>
 <p>
 In case of acting as a file handler, the handled file may need to be stored
 to access it after either a reboot, or suspending and resuming an event page
 of the providing extension. In such case
 <a href="fileSystem#method-retainEntry">chrome.fileSystem.retainEntry</a> and
 <a href="fileSystem#method-restoreEntry">chrome.fileSystem.restoreEntry</a>
 should be used.
 </p>