Add Licensing information to README

Docker-DCO-1.1-Signed-off-by: Vincent Mayers vince.mayers@gmail.com (github: vincentmayers)
[solomon@docker.com: rephrased commit message and transcribed signoff]
Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Merge pull request #5802 from shykes/pr_out_add_licensing_information_to_readme

Add Licensing information to README