Update README.md (#1310)

The old link to Mulan Public license is 404.
Co-authored-by: NLIN <wangzelin19961202@gmail.com>

README.md

@@ -44,6 +44,8 @@ For our success stories, see [Success stories](https://www.oceanbase.com/en/cust
 
 Your contributions to our code will be highly appreciated. For details about how to contribute to OceanBase, see [Contribute to OceanBase](https://github.com/oceanbase/oceanbase/wiki/Contribute-to-OceanBase).
 
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 ## Licensing
 
 OceanBase Database is licensed under the Mulan Public License, Version 2. See the [LICENSE](LICENSE) file for more info.