Create empty changelog for sros2_cmake.

sros2_cmake/CHANGELOG.rst

+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Changelog for package sros2_cmake
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+0.6.1 (2019-01-15)
+------------------
+
+0.6.0 (2018-12-07)
+------------------
+
+0.5.0 (2018-06-27)
+------------------
+
+0.4.0 (2017-12-08)
+------------------