minor change - lesson: crafting containers by hand - namespaces

[patrick-plue]

I think there is a minor logical mistake in the chapter: safety with namespaces.

In the last exercise it is instructed to run ps from # 1 to grab the pid for tail. This is not possible because we just isolated this environment and the tail process is running in # 2.
I suppose it would be better to change these instructions to grab the pid from # 2 and try to kill the process from # 1.