https://letsencrypt.org/documents/LE-SA-v1.1.1-August-1-2016.pdf
diff between version 1.0.1 and 1.1.1 of the agreement: https://gist.github.com/kennwhite/9541c8f37ec2994352c4554ca2afeece/revisions
Gist: "Lets Encrypt Subscriber Agreement"