I didn't see it originally but a colleague did see a unclear part using the words Ruby shell:
"Failure to log out and back into the Ruby shell results in an error reporting the Ruby gem bundle is locked. In this situation, do not run the bundle install command as instructed by the shell, as CloudForms uses yum to install gems.
"Failure to log out of the old shell environment and back into a new one results in an error reporting the Ruby gem bundle is locked.
"To resolve errors from running bundle install or failing to log in and out of Ruby: log out of Ruby and log back in, then run yum reinstall cfme-gemset."
"... failing to log in and out of the old shell environment: log out of the current shell and log back in, then run yum reinstall cfme-gemset"
Many thanks for the review/revision, Joe! That sounds a lot better -- it's not language I use frequently :)
I've cherry-picked this to the 4.5 and 4.2 migration guides, and the changes are live on the Portal: