Update upgrade-op-contracts-1-3-1-8.mdx

Author: Wazabie

pages/stack/smart-contracts/upgrade-op-contracts-1-3-1-8.mdx

@@ -27,6 +27,8 @@ This guide provides specific instructions for upgrading the OP Stack's Layer 1 c
 
 The Holocene upgrade is a protocol upgrade. Learn more about it in the [Holocene notice page](https://docs.optimism.io/notices/holocene-changes). This guide shows you how to take your OP Stack chain from the L2 Output Oracle System to a permissioned Fault Proof System contract version associated with the Holocene upgrade. 
 
+After upgrading to OP Stack contracts v1.8.0 and enabling permissioned fault proofs, all pending (unfinalized) withdrawal proofs created on L1 are invalidated. This means that withdrawals must be manually reproven by users after the upgrade; the process is not automatic.
+
 ### Formatting config files
 
 You need your chain's `deployments.json` and `deploy-config.json`