Add LZ4 NOTICE section from lucene to solr NOTICE.txt

Author: romseygeek

solr/NOTICE.txt

@@ -160,6 +160,11 @@ http://bitbucket.org/jpbarrette/moman/overview/
 The class org.apache.lucene.util.WeakIdentityMap was derived from
 the Apache CXF project and is Apache License 2.0.
 
+The class org.apache.lucene.util.compress.LZ4 is a Java rewrite of the LZ4
+compression library (https://github.com/lz4/lz4/tree/dev/lib) that is licensed
+under the 2-clause BSD license.
+(https://opensource.org/licenses/bsd-license.php)
+
 The Google Code Prettify is Apache License 2.0.
 See http://code.google.com/p/google-code-prettify/