Update links in the README (#56)

The specification in the sig-events repo is deprecated and should
not be linked to anymore.
Add links to the current primer and spec instead.

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

Author: afrittoli

README.md

@@ -57,4 +57,5 @@ If you would like to contribute, see our [development](DEVELOPMENT.md) guide.
 ## References
 
 - [CDEvents](https://cdevents.dev)
-- [CDFoundation SIG Events Vocabulary Draft](https://github.com/cdfoundation/sig-events/tree/main/vocabulary-draft)
+- [CDEvents Primer](https://cdevents.dev/docs/primer/)
+- [CDFoundation Specification](https://cdevents.dev/docs/)