pc-bios: Update README (SeaBIOS)

The PC BIOS no longer comes from Bochs.
This patch updates the related entry.

V2 - Modify SeaBIOS description and URL
     (Thanks to Gleb Natapov for the hint).
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

pc-bios/README

-- The PC BIOS comes from the Bochs project (http://bochs.sourceforge.net/).
+- SeaBIOS (bios.bin) is the successor of pc bios.
+  See http://www.seabios.org/ for more information.
 
 - The VGA BIOS and the Cirrus VGA BIOS come from the LGPL VGA bios
   project (http://www.nongnu.org/vgabios/).