Fix documentation for FSP API.

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

 <h2 id="manifest">Manifest</h2>
 <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 {{platform}}",
   ...
   "permissions": [
     "fileSystemProvider"
   ],
   ...
-  "file_system_provider_capabilities": [
+  "file_system_provider_capabilities": {
     "configurable": true,
     "multiple_mounts": true,
     <span id="manifest-source">"source": "network"</span>
-  ],
+  },
   ...
 }
 </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>
 <p>
@@ skipping 83 matching lines @@
 extension is unloaded, or the extension calls the $(ref:unmount) method.
 </p>
 {{?is_apps}}
 <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 $(ref:fileSystem.retainEntry) and
 $(ref:fileSystem.restoreEntry) should be used.
 </p>
 {{/is_apps}}