Document the limit on the number of parameters

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/10/static/sql-prepare.html
Description:

The backend protocol limits the number of parameters that can be passed for
a prepared statement to 32767 (2 byte signed integer).

As that is something that is independent of the client library, I think this
should be documented in the user facing manual for the Postgres server
somewhere. 

I did not find anything in the chapter about PREPARE
https://www.postgresql.org/docs/current/static/sql-prepare.html or about the
backend protocol:
https://www.postgresql.org/docs/current/static/protocol.html nor on the FAQ
page: https://wiki.postgresql.org/wiki/FAQ