Add step-by-step instructions for updating ruby gems.
Add step-by-step instructions for updating ruby gems.

Signed-off-by: Lincoln Baker <9097625024889eb4c0cbc9c268b49e14d04af1af@chef.io>

chef/chef-server,chef/chef-server,chef/chef-server,chef/chef-server,chef/chef-server,chef/chef-server