fix: Fix protocol docs url

Author: zguesmi

README.md

@@ -38,7 +38,7 @@ This repository contains the smart contract implementation of iExec's PoCo proto
 
 - [Solidity API documentation](./docs/solidity/index.md)
 <!-- TODO update with new documentation URL -->
-- [Full PoCo documentation](https://protocol.docs.iex.ec/key-concepts/proof-of-contribution)
+- [Full PoCo documentation](https://docs.iex.ec/protocol/proof-of-contribution)
 
 ## Audits