Update docker? help comment to show it's since 12.11
Update docker? help comment to show it's since 12.11

We've had this in chef/chef since 12.11. True it's only been in
chef-utils since 15.5. This led a community member to believe they
couldn't use it since they required Chef 13+. We should make sure folks
know they can use this helper.

Signed-off-by: Tim Smith <764ef62106582a09ed09dfa0b6bff7c05fd7d1e4@chef.io>

higanworks/chef,chef/chef,jaymzh/chef,mattray/chef,gene1wood/chef,nvwls/chef,higanworks/chef,nvwls/chef,mattray/chef,mattray/chef,jaymzh/chef,gene1wood/chef,tas50/chef-1,gene1wood/chef,jaymzh/chef,chef/chef,mwrock/chef,mwrock/chef,higanworks/chef,MsysTechnologiesllc/chef,nvwls/chef,nvwls/chef,MsysTechnologiesllc/chef,MsysTechnologiesllc/chef,mwrock/chef,nvwls/chef,tas50/chef-1,mwrock/chef,chef/chef,higanworks/chef,MsysTechnologiesllc/chef,chef/chef,nvwls/chef,tas50/chef-1,jaymzh/chef,tas50/chef-1,gene1wood/chef,mattray/chef,higanworks/chef,mattray/chef