Update holocene-changes.mdx

adding governance post link

Author: sbvegan

pages/builders/notices/holocene-changes.mdx

@@ -16,7 +16,7 @@ If you experience difficulty at any stage of this process, please reach out to [
 
   The Holocene upgrade for the Unichain Sepolia will be activated at **Wed Dec 18 at 22:00:00 UTC** (`1734559200`).
 
-  The Holocene upgrade for the Mainnet Superchain is optimistically scheduled for **Thu 9 Jan 2025 18:00:01 UTC**, pending governance approval.
+  The Holocene upgrade for the Mainnet Superchain is optimistically scheduled for **Thu 9 Jan 2025 18:00:01 UTC**, [pending governance approval](https://gov.optimism.io/t/upgrade-proposal-11-holocene-network-upgrade/9313).
 </Callout>
 
 ## What's included in Holocene