Add 4.6.1 section to CHANGES.txt

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1568316 13f79535-47bb-0310-9956-ffa450edef68
SOLR-1301: Add some readme files.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1568317 13f79535-47bb-0310-9956-ffa450edef68
SOLR-1301: Fix spelling.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1568328 13f79535-47bb-0310-9956-ffa450edef68