Fix broken example in docs
Fix broken example in docs

Must specify the primary hash key in local indexes, or you get `boto.dynamodb2.exceptions.ValidationException: ValidationException: 400 Bad Request`.
abridgett/boto,SaranyaKarthikeyan/boto,acourtney2015/boto,nexusz99/boto,podhmo/boto,vishnugonela/boto,elainexmas/boto,trademob/boto,Asana/boto,yangchaogit/boto,zachmullen/boto,ramitsurana/boto,alfredodeza/boto,israelbenatar/boto,felix-d/boto,pfhayes/boto,dimdung/boto,vijaylbais/boto,awatts/boto,stevenbrichards/boto,j-carl/boto,jindongh/boto,bleib1dj/boto,ekalosak/boto,ocadotechnology/boto,darjus-amzn/boto,khagler/boto,revmischa/boto,jotes/boto,bryx-inc/boto,rayluo/boto,Pretio/boto,TiVoMaker/boto,nikhilraog/boto,janslow/boto,rosmo/boto,garnaat/boto,campenberger/boto