Usermode containers

[kousu]

Edit the wiki to explain how to use containers on our linux systems.

We have podman installed which:

• is configured to allow unprivileged users to safely run containers
• stores its data under each user's ~/.local/share

Explain:

• how to get into a container
• how to make a container persistent vs ephemeral
• how to monitor disk usage -- the user ID trickery that containers do makes it hard to monitor your own quota
• how to clean up after yourself
• how to X forward into a container
• how to volume mount
• other things?

[kousu]

This mirrors #105 -- that makes full VMs, podman makes lightweight VMs. They're both useful in similar ways.

We should also probably explain, lightly, when you would prefer one or the other.