Improve documentation for --connect-shell option of the container launcher

[M4rtinK]

Right not it is not very clear how the --connect-shell should be used.

I think we should:

• improve the doc string to make it clear it is supposed to be combined with other options and it will not launch the container shell without it
• add an example of end to end usage to our docs

[rvykydal]

We have this doc so far:
https://github.com/rhinstaller/kickstart-tests/tree/main/containers/runner#running-test-manually-from-the-container