Improvements for the coreboot v2 README:

Improvements for the coreboot v2 README:

 - Point to the 'Payloads' wiki page for more info.

 - Document (most of) the build requirements of v2.

 - Point to the wiki for build instructions (wiki needs more docs, though).

 - Mention QEMU for testing coreboot, also point to wiki page.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Uwe Hermann <uwe@hermann-uwe.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4130 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1