Please add LICENSE

[gmacario]

Hello,

I learned about this repository during the Jenkins Meetup last week.

Thanks for putting this out, I have cloned your repo and am extending it with some additional pipelines which I will use as a test suite for my https://github.com/gmacario/easy-jenkins project.

May I kindly ask you to select a LICENSE add it it to the repository?
If you do not mind I would suggest the MIT license.

Thanks again for your instructive walk-through on Jenkins pipelines.