Add harlowja to credits in README
Add harlowja to credits in README

adamchainz/pymemcache,dive-tv/pyelasticache_client,pinterest/pymemcache,sontek/pymemcache,bwalks/pymemcache,mbrukman/pymemcache,ewdurbin/pymemcache,duanhongyi/pymemcache,pinterest/pymemcache,methane/pymemcache,thedrow/pymemcache,harlowja/pymemcache,sontek/pymemcache