Added README.md documentation for the GithubReleaseNotesGenerator
Added README.md documentation for the GithubReleaseNotesGenerator

cdcarter/CumulusCI,e02d96ec16/CumulusCI,SalesforceFoundation/CumulusCI,e02d96ec16/CumulusCI,Joble/CumulusCI,SalesforceFoundation/CumulusCI