MINOR: Add missing option for running vagrant-up.sh with AWS to vagrant/README.md
MINOR: Add missing option for running vagrant-up.sh with AWS to vagrant/README.md

Contrary to the previous explanation, a command example in
vagrant/README.md lacks the option to specify the aws provider.

Author: Kengo Seki <sekikn@apache.org>

Reviewers: Gwen Shapira

Closes #6702 from sekikn/add-missing-option

guozhangwang/kafka,lindong28/kafka,noslowerdna/kafka,TiVo/kafka,Chasego/kafka,Chasego/kafka,guozhangwang/kafka,sslavic/kafka,guozhangwang/kafka,KevinLiLu/kafka,noslowerdna/kafka,TiVo/kafka,apache/kafka,TiVo/kafka,sslavic/kafka,KevinLiLu/kafka,guozhangwang/kafka,apache/kafka,noslowerdna/kafka,sslavic/kafka,apache/kafka,apache/kafka,KevinLiLu/kafka,TiVo/kafka,lindong28/kafka,Chasego/kafka,noslowerdna/kafka,lindong28/kafka,lindong28/kafka,Chasego/kafka,sslavic/kafka,KevinLiLu/kafka