update license

database/README.md

@@ -63,3 +63,12 @@ Notes: To have a large global memory space, you may need to modify size in 'incl
 # Acknowledgement #
 This implementation is adapted from an open-source transactional database prototype on single machines:
 https://github.com/Cavalia/Cavalia
+
+The license of Cavalia is attached bellows.
+
+Copyright (C) 2015-16, School of Computing, National University of Singapore
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.