provider/vault: Add vault_policy to documentation sidebar (hashicorp#11912)

Author: stack72

website/source/layouts/vault.erb

@@ -29,6 +29,10 @@
                             <a href="/docs/providers/vault/r/generic_secret.html">vault_generic_secret</a>
                         </li>
 
+                        <li<%= sidebar_current("docs-vault-resource-policy") %>>
+                            <a href="/docs/providers/vault/r/policy.html">vault_policy</a>
+                        </li>
+
                     </ul>
                 </li>