Fix directive example to match description
Fix directive example to match description

The description claims the directive is appearing after a comment but
the sample Dockerfile has the directive appear after an instruction.
Changed the ordering of the lines to match the example's description.

Signed-off-by: Remy Suen <553f7e7fc51e9ff47ae89d5a0ebd06651241b998@gmail.com>
cpuguy83/cli,Zebrilee/cli,allencloud/cli,e11137/cli,redpanda/cli,thaJeztah/cli,cpuguy83/cli,docker/cli,allencloud/cli,Zebrilee/cli,dnephin/cli,dnephin/cli,riyazdf/cli,ashfall/cli,docker/cli,ashfall/cli,riyazdf/cli,thaJeztah/cli,redpanda/cli,e11137/cli