RE: doc: clarify the limitation for logical replication when REPILICA IDENTITY is FULL

Dear Sergei,

Thank you for giving comment!

The restriction is only for subscriber: the publisher can publish the changes
to downstream under the condition, but the subscriber cannot apply that.

> So, I suggest to mention subscriber explicitly:
> 
> +     class of Btree, then <literal>UPDATE</literal> and
> <literal>DELETE</literal>
> -      operations cannot be replicated.
> +     operations cannot be applied on subscriber.

I accepted the comment. Please see [1].

[1]:
https://www.postgresql.org/message-id/TYAPR01MB58664DB6ECA653A6922B3FE3F531A%40TYAPR01MB5866.jpnprd01.prod.outlook.com

Best Regards,
Hayato Kuroda
FUJITSU LIMITED