fix: expose timepicker

Exposes the timepicker in the docs.

Author: crisbeto

material.angular.io/material.angular.io/src/app/shared/documentation-items/documentation-items.ts

@@ -357,6 +357,15 @@ const DOCS: { [key: string]: DocItem[] } = {
       },
       additionalApiDocs: [{name: 'Testing', path: 'material-tabs-testing.html'}],
     },
+    {
+      id: 'timepicker',
+      name: 'Timepicker',
+      summary: 'Allows the user to select a time of the day.',
+      exampleSpecs: {
+        prefix: 'time',
+      },
+      additionalApiDocs: [{name: 'Testing', path: 'material-timepicker-testing.html'}],
+    },
     {
       id: 'toolbar',
       name: 'Toolbar',