Fix broken link to migration for 1.X (#6174)

Author: zoenolan

README.md

@@ -43,7 +43,7 @@ yarn add web3
 
 ## Migration Guide
 
--   [Migration Guide from Web3.js 1.x to 4.x](https://docs.web3js.org/docs/guides/web3_migration_guide)
+-   [Migration Guide from Web3.js 1.x to 4.x](https://docs.web3js.org/guides/web3_upgrade_guide/x/)
     Breaking changes are listed in migration guide and its first step for migrating from Web3.js 1.x to 4.x. If there is any question or discussion feel free to ask in [Discord](https://discord.gg/yjyvFRP), and in case of any bug or new feature request [open issue](https://github.com/web3/web3.js/issues/new) or create a pull request for [contributions](https://github.com/web3/web3.js/blob/4.x/CONTRIBUTIONS.md).
 
 ## Useful links