Added GRUB docs, Added netboot.xyz

boot/grub/persistent/docs/10_vendor_poweron_keys

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+10 Using GRUB with vendor power-on keys
+***************************************
+
+Some laptop vendors provide an additional power-on button which boots
+another OS. GRUB supports such buttons with the 'GRUB_TIMEOUT_BUTTON',
+'GRUB_TIMEOUT_STYLE_BUTTON', 'GRUB_DEFAULT_BUTTON', and
+'GRUB_BUTTON_CMOS_ADDRESS' variables in default/grub (*note Simple
+configuration::).  'GRUB_TIMEOUT_BUTTON', 'GRUB_TIMEOUT_STYLE_BUTTON',
+and 'GRUB_DEFAULT_BUTTON' are used instead of the corresponding
+variables without the '_BUTTON' suffix when powered on using the special
+button.  'GRUB_BUTTON_CMOS_ADDRESS' is vendor-specific and partially
+model-specific.  Values known to the GRUB team are:
+
+<Dell XPS M1330M>
+     121:3
+<Dell XPS M1530>
+     85:3
+<Dell Latitude E4300>
+     85:3
+<Asus EeePC 1005PE>
+     84:1 (unconfirmed)
+<LENOVO ThinkPad T410s (2912W1C)>
+     101:3
+
+   To take full advantage of this function, install GRUB into the MBR
+(*note Installing GRUB using grub-install::).
+
+   If you have a laptop which has a similar feature and not in the above
+list could you figure your address and contribute?  To discover the
+address do the following:
+   * boot normally
+   *      sudo modprobe nvram
+          sudo cat /dev/nvram | xxd > normal_button.txt
+   * boot using vendor button
+   *      sudo modprobe nvram
+          sudo cat /dev/nvram | xxd > normal_vendor.txt
+
+   Then compare these text files and find where a bit was toggled.  E.g.
+in case of Dell XPS it was:
+     byte 0x47: 20 --> 28
+   It's a bit number 3 as seen from following table:
+0              01
+1              02
+2              04
+3              08
+4              10
+5              20
+6              40
+7              80
+
+   0x47 is decimal 71.  Linux nvram implementation cuts first 14 bytes
+of CMOS. So the real byte address in CMOS is 71+14=85 So complete
+address is 85:3
+