Update the main README to v0.3.0 as latest release

Signed-off-by: Andrea Frittoli <[email protected]>

Author: afrittoli

README.md

@@ -39,7 +39,7 @@ points for metrics.
 ## CDEvents Specification
 
 The latest release of the specification on is
-[v0.2.0](https://github.com/cdevents/spec/blob/v0.2.0/spec.md), and you can
+[v0.3.0](https://github.com/cdevents/spec/blob/v0.3.0/spec.md), and you can
 continuously follow the latest updates of the specification on [the `main`
 branch](./spec.md).