[CMake] Add missing license

benchmark/CMakeLists.txt

+#
+# Copyright (c) 2015-2016 CNRS
+#
+# This file is part of Pinocchio
+# pinocchio is free software: you can redistribute it
+# and/or modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation, either version
+# 3 of the License, or (at your option) any later version.
+# pinocchio 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. See the GNU
+# General Lesser Public License for more details. You should have
+# received a copy of the GNU Lesser General Public License along with
+# pinocchio If not, see
+# <http://www.gnu.org/licenses/>.
+
 # ----------------------------------------------------
 # --- BENCHMARK --------------------------------------
 # ----------------------------------------------------