[DOC] Xvisor v0.2.4 release notes

This patch adds release notes for upcoming v0.2.4 release.

Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[DOCS] x86: Detailed description of how to build and run Xvisor.

This includes compiling seabios and running it as guest.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
Merge remote-tracking branch 'upstream/master' into A20