Add customers to SUMMARY

Author: razor-x

docs/SUMMARY.md

@@ -225,6 +225,9 @@
   * [Update a Connected Account](api/connected_accounts/update.md)
   * [Delete a Connected Account](api/connected_accounts/delete.md)
   * [Sync a Connected Account](api/connected_accounts/sync.md)
+* [Customers](api/customers/README.md)
+  * [Create Customer Portal](api/customers/create_portal.md)
+  * [Push Customer Data](api/customers/push_data.md)
 * [Devices](api-clients/devices/README.md)
   * [List Devices](api-clients/devices/list.md)
   * [List Device Providers](api-clients/devices/list_device_providers.md)