Update README.md

The original text was NOT correct with respect tp Jenkins as referenced at the cited URL and twitter account, which is a no-cost, open source, MIT-licensed project available at https://github.com/jenkinsci/jenkins.git

The original text was correct with respect to http://www.cloudbees.com/ which is only one of a number (see https://wiki.jenkins-ci.org/display/JENKINS/Commercial+Support) of commercial Jenkins hosting / service providers (albeit the one with which the Jenkins developer is affiliated.)