Update REAMDE.md

Closes GH-28

README.md

@@ -22,6 +22,16 @@ detect the correct handle preceding _DSM and has some built-in safeguards:
   disabled again if that was the case before suspending. Hibernation should
   work, but it not tested.
 
+Precautionary measure : 
+- On some machines, turning off the card is permanent and the card does not
+  reappear on subsequents reboots, which can result into the screen staying
+  black all the time, including the BIOS screen.
+  If it occurs, first try to shutdown, unplug power cord, remove battery, wait
+  30s, then put everything back in and boot. If it's not solved, then the
+  solution is to reset the BIOS to factory settings. Before executing bbswitch
+  for the first time, it is therefore recommended to take note of the full key
+  sequence in the BIOS to do a reset. 
+
 Build
 -----
 
@@ -110,6 +120,17 @@ You have to update your initial ramdisk (initrd) for the changes propagate to
 the boot process. On Debian and Ubuntu, this can performed by running
 `update-initramfs -u` as root.
 
+### Enable card on shutdown
+
+Some machines do not like the card being disabled at shutdown.  
+Add the next initscript (`/etc/init/bbswitch.conf`) :
+     description "Save power by disabling nvidia on Optimus"
+     author      "Lekensteyn <lekensteyn@gmail.com>"
+     start on    runlevel [2345]
+     stop on     runlevel [016]
+     pre-start   exec /sbin/modprobe bbswitch load_state=0 unload_state=1
+     pre-stop    exec /sbin/rmmod bbswitch 
+
 Reporting bugs
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