chore: Add cpu-template-helper to changelog

Add an entry of the `cpu-template-helper` tool to CHANGELOG.md.

Now all the helper tool code required for Firecracker 1.4 release is
ready.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

CHANGELOG.md

@@ -8,6 +8,8 @@
   exposed to the guest via CPUID, MSRs and ARM registers.
 - Introduced V1N1 static CPU template for ARM to represent Neoverse V1 CPU
   as Neoverse N1.
+- Added a `cpu-template-helper` tool for assisting with creating and managing
+  custom CPU templates.
 
 ### Fixed