docs/backends: Update overview from bind.rst

According to bind.rst support for Autosecondary is "Experimental".
Claim the same in the overview table.

docs/backends/index.rst

@@ -6,7 +6,7 @@ The following table describes the supported backends and some of their capabilit
 +------------------------------------------------+--------+---------+-----------+----------+----------+---------------+----------------------------------+---------------------------------+--------------+
 | Name                                           | Native | Primary | Secondary | Producer | Consumer | Autosecondary | :doc:`DNS Update <../dnsupdate>` | :doc:`DNSSEC <../dnssec/index>` | Launch       |
 +================================================+========+=========+===========+==========+==========+===============+==================================+=================================+==============+
-| :doc:`BIND <bind>`                             | Yes    | Yes     | Yes       | No       | No       | Yes           | No                               | Yes                             | ``bind``     |
+| :doc:`BIND <bind>`                             | Yes    | Yes     | Yes       | No       | No       | Experimental  | No                               | Yes                             | ``bind``     |
 +------------------------------------------------+--------+---------+-----------+----------+----------+---------------+----------------------------------+---------------------------------+--------------+
 | :doc:`Generic Mysql/Mariadb <generic-mysql>`   | Yes    | Yes     | Yes       | Yes      | Yes      | Yes           | Yes                              | Yes                             | ``gmysql``   |
 +------------------------------------------------+--------+---------+-----------+----------+----------+---------------+----------------------------------+---------------------------------+--------------+