fix(CHANGELOG.unreleased): better syntax for variables

CHANGELOG.unreleased.md

@@ -22,15 +22,15 @@
 >
 > Rule of thumb: add packages on top.
 >
-> The format is the following: - <packageName> <version>
+> The format is the following: - `$packageName` `$version`
 >
-> Where <version> is
+> Where `$version` is
 >
 > - patch: if the change is a bug fix or a simple code improvement
 > - minor: if the change is a new feature
 > - major: if the change breaks compatibility
 >
-> In case of conflict, the highest (lowest in previous list) <version> wins.
+> In case of conflict, the highest (lowest in previous list) `$version` wins.
 
 - xen-api patch
 - xo-server patch