remove deletion of system instructions and add test file creation ins…

[pc-eficode]

…tead

Removed instructions to delete system binaries and added steps to create a test file.

[JKrag]

I understand that adding a file is a lot safer than doing an rm -rf 😉 , but it loses some of the effect of demonstrating that this is an isolated environment.
I would suggest at least that it would require a follow-up step to get the user to check that the new file is in fact not available in the new instance (and maybe show that it is not visible in the host fs either).