added hw4 spec
added hw4 spec

KenjiYoshikawa/saas-homework,rilian/saas-homework,lsx0519/saas-homework,rilian/saas-homework,lsx0519/saas-homework,lsx0519/saas-homework,KenjiYoshikawa/saas-homework,rilian/saas-homework,KenjiYoshikawa/saas-homework