update LICENSE to reflect the use of librhash code

LICENSE

@@ -21,3 +21,23 @@ HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 SUCH DAMAGE.
+
+-----
+Some code is adapted from librhash by Aleksey Kravchenko:
+https://github.com/rhash/RHash
+http://rhash.anz.ru/
+
+                                RHash License
+
+Copyright (c) 2005-2014 Aleksey Kravchenko <rhash.admin@gmail.com>
+
+Permission is hereby granted, free of charge,  to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction,  including without limitation the rights
+to  use,  copy,  modify,  merge, publish, distribute, sublicense, and/or sell
+copies  of  the Software,  and  to permit  persons  to whom  the Software  is
+furnished to do so.
+
+The Software  is distributed in the hope that it will be useful,  but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+FOR A PARTICULAR PURPOSE.  Use  this  program  at  your  own  risk!