docs: Add OpenSSL exemption to license

Change-Id: If03222c482655f78c6b7343122e40323723df419
diff --git a/COPYING.md b/COPYING.md
index d799430..a3872f1 100644
--- a/COPYING.md
+++ b/COPYING.md
@@ -1,3 +1,48 @@
+NLSR LICENSE
+============
+
+NLSR is released under the GPL with the additional exemption that
+compiling, linking, and/or using OpenSSL is allowed.
+
+NLSR relies on third-party software and libraries, licensed under the following
+licenses:
+
+- Boost libraries are licensed under the conditions of
+  [Boost Software License 1.0](http://www.boost.org/users/license.html)
+
+- CryptoPP library is licensed under the conditions of
+  [Boost Software License 1.0](http://www.boost.org/users/license.html)
+
+- log4cxx is licensed under the conditions of
+  [Apache License, Version 2.0](https://logging.apache.org/log4cxx/license.html)
+
+- ndn-cxx is licensed under the conditions of
+  [LGPL 3.0](https://github.com/named-data/ndn-cxx/blob/master/COPYING.md)
+
+- protobuf is licensed under the conditions of
+  [BSD license](https://github.com/google/protobuf/blob/master/LICENSE)
+
+- SQLite is in [public domain](http://www.sqlite.org/copyright.html)
+
+- waf build system is licensed under the conditions of
+  [BSD license](https://github.com/named-data/ndn-cxx/blob/master/waf)
+
+NLSR also relies on third-party libraries with non-GPL compatible licenses.
+These libraries fall into the category of "System Libraries" under GPL
+license definitions and are used in accordance with the GPL license exception
+for "System Libraries":
+
+- OpenSSL is licensed under an
+  [Apache-style licence](http://www.openssl.org/source/license.html)
+
+- (OS X platform only) OS X Security Framework is licensed under
+  [Apple Public Source License](http://www.opensource.apple.com/license/apsl/)
+
+The GPL license is provided below in this file.
+For more information, see http://www.gnu.org/licenses/
+
+----------------------------------------------------------------------------------
+
 GNU GENERAL PUBLIC LICENSE
 ==========================
 Version 3, 29 June 2007