Several fixups and new features

[bpkroth]

• Fixes a path change for checking whether the vmaccess extension exists
• Places the ssh proxy pod on the same node as the target.
  • For some reason this fixes a tty issue for me. I suspect it's related to an MTU between the pod and the target host, but that's not a thing I'd want to be messing with.
• Add a -p|--pod-name option to select the node to connect to by looking it up by a target user pod.
• Updates the README.md with new content and to address some markdown lint complaints.

[bpkroth]

Being a little lazy here and putting several changes in a single PR. Let me know if you want the individual commits broken up.