added mock example to README
added mock example to README

yaoshipu/testify,ANPez/testify,MCProHosting/testify,outrightmental/go-testify,mesosphere/testify,allgeek/testify,dvln/testify,grepory/testify,irnnr/testify,codygibb/testify,embroker/testify,ernesto-jimenez/testify,ifraixedes/testify,liudhzhyym/testify,danielchatfield/testify,hpcloud/testify,bmatsuo/testify,roth1002/testify,pki-io/testify,insionng/testify,andymoon/testify,AnuchitPrasertsang/testify,betable/testify,stretchr/testify,davelondon/ktest,Fiery/testify,wallclockbuilder/testify,csquared/testify,brahmaroutu/testify,glittershark/testify,hawx/assert,stretchr/testify,yxd-hde/testify,yxd-hde/testify,multiplay/testify