DL-4: Add NOTICE file.
DL-4: Add NOTICE file.

Author: Franck Cuny <fcuny@apache.org>

Reviewers: Sijie Guo <sijie@apache.org>

Closes #2 from franckcuny/fcuny/DL-4

twitter/distributedlog,twitter/distributedlog,sijie/incubator-distributedlog,twitter/distributedlog,sijie/incubator-distributedlog,twitter/distributedlog,sijie/incubator-distributedlog,sijie/incubator-distributedlog,sijie/incubator-distributedlog,twitter/distributedlog