docs: Improve pg_isready details about username/dbname

Report by Erik Rijkers

Backpatch through 9.4

doc/src/sgml/ref/pg_isready.sgml

@@ -170,8 +170,9 @@ PostgreSQL documentation
   <title>Notes</title>
 
   <para>
-   The options <option>--dbname</> and <option>--username</> can be used to avoid gratuitous
-   error messages in the logs, but are not necessary for proper functionality.
+   It is not necessary to supply correct user name, password, or database
+   name values to obtain the server status; however, if incorrect values
+   are provided, the server will log a failed connection attempt.
   </para>
  </refsect1>