hacking.md: more details about TANGLED_VM_SPINDLE_OWNER
I think it'd be nice to make setting `TANGLED_VM_SPINDLE_OWNER`
optional and run VMs without a spindle in that case, but
let's just document the status quo for now.
Signed-off-by: Ilya Grigoriev <ilyagr@users.noreply.github.com>
authored by