Fix doc bug in logical replication.

Howdy folks,

I noticed that the docs currently state "A different order of columns
in the target table is allowed, but the column types have to match."
This is untrue, as you can replicate between any two data types as
long as the data can be coerced into the right format on the
subscriber. Attached is a patch that attempts to clarify this, and
provides some additional wordsmithing of that section. Patch is
against head but the nature of the patch would apply to the docs for
11 and 10, which both have the incorrect information as well, even if
the patch itself does not.

Robert Treat
https://xzilla.net