Update README to reflect default sudoers groups
Update README to reflect default sudoers groups

Per attributes/default.rb line 19, default is 'sysadmin'
chef-cookbooks/sudo,itwasntandy/sudo,itwasntandy/sudo,opscode-cookbooks/sudo,bcg62/sudo,spheromak/sudo,chef-cookbooks/sudo,cringdahl/sudo,opscode-cookbooks/sudo,spheromak/sudo,opscode-cookbooks/sudo,autarchprinceps/sudo,cringdahl/sudo,juliandunn/sudo,itwasntandy/sudo,juliandunn/sudo,autarchprinceps/sudo,bcg62/sudo,spheromak/sudo