update README with beagle_bx change

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

README

@@ -1,4 +1,4 @@
-git://github.com/RobertCNelson/netinstall-omap.git
+git clone git://github.com/RobertCNelson/netinstall-omap.git
 cd netinstall-omap
 ./mk_mmc.sh --mmc /dev/sdX --uboot <dev board> --distro <distro> --firmware
 
@@ -7,7 +7,8 @@ Required Options:
     Unformated MMC Card
 
 --uboot <dev board>
-    beagle - <Bx, Cx, xM A/B/C>
+    beagle_bx - <Ax/Bx Models>
+    beagle - <Cx, xM A/B/C>
     panda - <dvi or serial>
     touchbook - <serial only>