CHANGELOG: Mention PVH boot mode

Firecracker now supports PVH boot as an alternative to "Linux" boot on
the x86_64 architecture.  This makes it possible for FreeBSD to boot,
and also affects how Linux kernels compiled with the CONFIG_XEN_PVH=y
option boot.

Signed-off-by: Colin Percival <[email protected]>

Author: cperciva

CHANGELOG.md

@@ -192,6 +192,10 @@ and this project adheres to
   [random for clones](docs/snapshotting/random-for-clones.md) documention for
   more info on VMGenID. VMGenID state is part of the snapshot format of
   Firecracker. As a result, Firecracker snapshot version is now 2.0.0.
+- Added support for PVH boot mode.  This is used when an x86 kernel provides
+  the appropriate ELF Note to indicate that PVH boot mode is supported.
+  Linux kernels compiled with CONFIG_XEN_PVH=y set this ELF Note, as do
+  FreeBSD kernels.
 
 ### Changed