Update pg_hba.conf comment about documentation section.

src/backend/libpq/pg_hba.conf.sample

 # PostgreSQL Client Authentication Configuration File
 # ===================================================
 #
-# Refer to the PostgreSQL Administrator's Guide, chapter "Client
-# Authentication" for a complete description.  A short synopsis
-# follows.
+# Refer to the "Client Authentication" section in the
+# PostgreSQL documentation for a complete description
+# of this file.  A short synopsis follows.
 #
 # This file controls: which hosts are allowed to connect, how clients
 # are authenticated, which PostgreSQL user names they can use, which