update readme for block based coverage
update readme for block based coverage

jacksonpradolima/pitest,artspb/pitest,jacksonpradolima/pitest,mzw/pitest,august782/pitest,artspb/pitest,lkwg82/pitest,jasonmfehr/pitest,velo/pitest,mzw/pitest,hcoles/pitest,artspb/pitest,jasonmfehr/pitest,velo/pitest,august782/pitest,hcoles/pitest,jasonmfehr/pitest,august782/pitest,velo/pitest,mzw/pitest,lkwg82/pitest,lkwg82/pitest,jacksonpradolima/pitest