feat(docs): dynDNS: explain how to update multiple subdomains

docs/dyndns/configure.rst

@@ -160,3 +160,16 @@ documentation.
 
 To test your setup, run ``sudo ddclient -force`` and see if everything works as
 expected.
+
+
+.. _updating-multiple-dyn-domains:
+
+Updating multiple domains
+`````````````````````````
+To update multiple domain or subdomains, it is best to designate one of them
+as the main domain, and create CNAME records for the others, so that they act
+as DNS aliases for the main domain.
+You can use do that either via the web interface or the API.
+
+If you try to update several subdomains directly (by issuing multiple update
+requests), your update requests may be refused (see :ref:`rate-limits`).

docs/dyndns/update-api.rst

@@ -100,6 +100,9 @@ Authentication.  In this case, replace your authentication username with
 ``sub.yourdomain.dedyn.io``.  Similarly, if you use the ``hostname`` query
 parameter, it needs to be set to the full domain name (including subdomain).
 
+To update more than one domain name, please see
+:ref:`updating-multiple-dyn-domains`.
+
 .. _determine-ip-addresses:
 
 Determine IP addresses

docs/rate-limits.rst

@@ -31,8 +31,7 @@ the API.  When several rates are given, all are enforced at the same time.
 +--------------------------------+----------+-------------------------------------------------------------------------------------------+
 | ``account_management_passive`` | 10/min   | Account activities with internal effects (e.g. viewing account details, creating a token) |
 +--------------------------------+----------+-------------------------------------------------------------------------------------------+
-| ``dyndns``                     | 1/min    | dynDNS updates (per domain).  If you need to keep subdomains in sync, consider setting up |
-|                                |          | a ``CNAME`` redirect in our web interface.                                                |
+| ``dyndns``                     | 1/min    | dynDNS updates (per domain).                                                              |
 +--------------------------------+----------+-------------------------------------------------------------------------------------------+
 | ``dns_api_read``               | 10/s     | DNS read operations (e.g. fetching an RRset)                                              |
 |                                |          |                                                                                           |