[PATCH][Documination] Add optional USING keyword before opclass name in INSERT statemet

If I read gram.y code for insert statement, I see that there is an optional
USING keyword before opclass name


opt_class:  any_name                                { $$ = $1; }
            | USING any_name                        { $$ = $2; }
            | /*EMPTY*/                             { $$ = NIL; }
        ;

but it the documentation this keyword is omitted.

I'd like to offer a patch that fixes this problem

--
Nikolay Shaplov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company