v2v: Remove documentation about Windows Recovery Console not supported.

We have now successfully converted guests using WRC, so this statement
is no longer necessary.
v2v: Add documentation about what to do about BSOD 0x0000007B (RHBZ#1161333).

After a very long and trying episode with a Windows guest that refused
to boot after conversion, we managed to successfully boot it by
disabling Windows Group Policy.  It appears that Group Policy
prevented the virtio driver from being used.

Document this in the manual.