Fix typo in docs for docker run -dns
Adding a reference to ps -a

It was confusing to me as a first-time user that my docker attach command failed; I was expecting the container to run continuously, and when I couldn't attach to it, I assumed something was wrong. ps -a shows that the container still exists, which gives the user confidence to go to the next step.
Merge pull request #1499 from seldo/master

* Documentation: Adding a reference to ps -a
Merge pull request #1494 from KSid/typo-docs-run-command

* Documentation: Fix typo in docs for docker run -dns