in an initramfs, then transition to the real root filesystem. Useful
for systems requiring early boot tasks like LUKS unlock, LVM activation,
or network boot before mounting the real root.
Adds INIT_CMD_SWITCH_ROOT API command, `initctl switch-root` subcommand,
and HOOK_SWITCH_ROOT plugin hook point. The implementation gracefully
stops services, moves virtual filesystems (/dev, /proc, /sys, /run) to
the new root, deletes initramfs contents to free memory, then execs the
new init as PID 1.
See GitHub Discussion #292 for background.
Try out navigation.tabs, if we don't like it we can revert.
Reorg for stricter sections, what information actually belongs where?
E.g., introduction is now in a Getting Started section.
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>