LXC/Getting started: Add --clear-env flag to lxc-attach to prevent common roadblock for newcomers.

[nordtektiger]

This patch adds --clear-env to every invocation of lxc-attach in the Getting Started page for LXC. The omission of this flag can cause issues on certain distributions and since this page does not seem to utilize the passing of environment variables to the container, simply adding the flag strikes me as a trivial solution. See #796 for more details.

Happy to revise this patch as the maintainers see fit.

[stgraber]

Your commit is missing the required Signed-off-by string in the commit message, could you add that?

[nordtektiger]

The commit is, in fact, signed off, albeit using my real name rather than my username. The contributing.md file stated that "no pseudonyms or anonymous contributions are allowed," which is why I changed it to say Jacob Aulin instead of nordtektiger. This seems to have tripped the GitHub action?

I could absolutely go back and amend the commit, changing it into my username instead if that's preferable. I guess the contribution specification is just a little unclear regarding the DCO, in that case.

Do let me know if it's passable as is, or if I should amend the commit message. Thank you for maintaining the linuxcontainers.org website, by the way, I greatly appreciate it.

[stgraber]

Ah, that's fine, it's just the checker being overly pick about the two fields lining up :)