Patch: doc for pg_logical_emit_message()

Hi, Hackers

pg_logical_emit_message() can be used by any user,
but the following document says that it can be used by only superuser.

> Table 9.88. Replication SQL Functions
> Use of these functions is restricted to superusers.

I think that pg_logicl_emit_message() should be used by any user.
Therefore, I attach the document patch.

Ryo
Matsumura