Fix incorrect path in ENTRYPOINT example

The ENTRYPOINT example uses "/usr/bin/ls" as path, but `ls` is located at `/bin/ls`.

Docker-DCO-1.1-Signed-off-by: Sebastiaan van Stijn <github@gone.nl> (github: thaJeztah)
Merge pull request #7185 from thaJeztah/patch-1

Fix incorrect path in ENTRYPOINT example