Update readme, make it more clear to use httptest
Update readme, make it more clear to use httptest

Fix #64

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