README: Further cleanup and refactoring

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

doc/signals.md

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+Finit Signals
+=============
+
+Finit is often used on embedded and small Linux systems with BusyBox.
+Though Finit comes with its own tools for (poweroff, halt, reboot), for
+compatibility with the existing BusyBox toolset the following signals
+have been adopted:
+
+* `SIGUSR1`  
+  Same effect as `finit q`, reloads all *.conf files in `/etc/finit.d/`
+* `SIGUSR1`  
+  Calls shutdown hooks, including HOOK_SHUTDOWN, stops all running
+  processes, and unmounts all file systems.  Then tells kernel to
+  halt.  Most people these days want SIGUSR2 though.
+
+  SysV init and systemd use this to re-open their FIFO/D-Bus.
+* `SIGUSR2`  
+  Like SIGUSR1, but tell kernel to power-off the system, if ACPI
+  or similar exists to actually do this.  If the kernel fails
+  power-off, Finit falls back to halt.
+ 
+  SysV init N/A, systemd dumps its internal state to log.
+* `SIGTERM`  
+  Like `SIGUSR1`, but tell kernel to reboot the system when done.
+ 
+  SysV init N/A, systemd rexecutes itself.
+* `SIGINT`  
+  Sent from kernel when the CTRL-ALT-DEL key combo is pressed.
+  SysV init and systemd default to reboot with `shutdown -r`.  
+  Finit currently forwards this to `SIGTERM`.
+* `SIGPWR`  
+  Sent from a power daemon, like `powstatd(8)`, on changes to the
+  UPS status.  Traditionally SysV init read /etc/powerstatus and
+  acted on "OK", "FAIL", or "LOW" and then removed the file.  
+  Finit currently forwards this to `SIGUSR2`.
+
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