Fix pull through guide description. (#1738)

Fix description (was cut & paste of cloud events)

Signed-off-by: Adrian Mouat <[email protected]>

content/chainguard/chainguard-registry/pull-through-guides/_index.md

@@ -9,4 +9,5 @@ images: []
 weight: 100
 ---
 
-Documentation and resources explaining what Chainguard [CloudEvents](https://cloudevents.io/) are and how to use them.
+Documentation and resources explaining how to set-up various third-party registries as pull-through caches
+or mirrors of the Chainguard registry.