Added note about license in CONTRIBUTING (#724)
Added note about license in CONTRIBUTING (#724)

Added note that any code or documentation modification done in the
repository shall be published in Apache 2.0 license.

Signed-off-by: Maciej Patelczyk <dab3e64c9b6ff7dce28693076765b4373d8dfee7@intel.com>
intelsdi-x/swan,intelsdi-x/swan,intelsdi-x/swan