coreos-download: add release note section
    
    Adds a release note section on the overview page of Fedora CoreOS
    Download. This gives users general information about the last
    5 releases for each of stable, testing and next stream.
    
    For each release, list the versions of important packages and package
    information about what was added, removed, upgraded and downgraded. In
    addition, for future improvements, adding notes on bugfix information
    might also be helpful.
    
    Signed-off-by: Allen Bai <abai@redhat.com>