doc: massive refactor and simplification to migrate to mkdocs

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/commands.md

@@ -0,0 +1,13 @@
+Rebooting & Halting
+===================
+
+Traditionally, rebooting and halting a UNIX system is done by switching
+to the corresponding runlevel (0 or 6).  Over time this has changed and
+Finit comes with its own tooling providing: `shutdown`, `reboot`,
+`poweroff`, and `suspend`.  These commands are also available from the
+[`initctl`](initctl.md) tool.
+
+For compatibility reasons Finit listens to the same set of signals as
+BusyBox init.  This is not 100% compatible with SysV init, but clearly
+the more common combination for Finit.  For more details, see the
+[Signal](signals.md) section.