add link to paper

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1619226 13f79535-47bb-0310-9956-ffa450edef68
sync rjernst's r1618245 change to lucene/CHANGES.txt with Solr's copy (smokecheck verification failure) (merge r1619225)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1619228 13f79535-47bb-0310-9956-ffa450edef68