[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