Include libunwind license in LICENSE file.

Change-Id: I53fa64deaf67746720c7baa7e22b3d7121076166
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/2304009
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
diff --git a/LICENSE b/LICENSE
index 95207bd..3486384 100644
--- a/LICENSE
+++ b/LICENSE
@@ -48,3 +48,29 @@
 Unicode Standard, and to make copies of this file in any form
 for internal or external distribution as long as this notice
 remains attached.
+
+--------------------------------------------------------------------
+
+libunwind - a platform-independent unwind library
+   Copyright (C) 2008 Google, Inc
+	Contributed by Paul Pluzhnikov <ppluzhnikov@google.com>
+   Copyright (C) 2010 Konstantin Belousov <kib@freebsd.org>
+
+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, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */