Update testing instructions in the README after the Solr mirror went away
Update testing instructions in the README after the Solr mirror went away

This uses the canonical Apache archive which should be more stable than the mirror we were using
upayavira/pysolr,upayavira/pysolr,django-searchstack/skisolr,mbeacom/pysolr,django-haystack/pysolr,mylanium/pysolr,10clouds/pysolr,mbeacom/pysolr,shasha79/pysolr,swistakm/pysolr,django-haystack/pysolr,CANTUS-Project/pysolr-tornado,swistakm/pysolr,CANTUS-Project/pysolr-tornado,toastdriven/pysolr,rokaka/pysolr,shasha79/pysolr,django-searchstack/skisolr,rokaka/pysolr,toastdriven/pysolr,10clouds/pysolr,mylanium/pysolr