fix wrong link to CONTRIBUTING.md

it led to CHANGELOG.md

Author: arnehormann

README.md

@@ -297,7 +297,7 @@ To run the driver tests you may need to adjust the configuration. See the [Testi
 Go-MySQL-Driver is not feature-complete yet. Your help is very appreciated.
 If you want to contribute, you can work on an [open issue](https://github.com/go-sql-driver/mysql/issues?state=open) or review a [pull request](https://github.com/go-sql-driver/mysql/pulls).
 
-See the [Contributing Guidelines](https://github.com/go-sql-driver/mysql/blob/master/CHANGELOG.md) for details.
+See the [Contribution Guidelines](https://github.com/go-sql-driver/mysql/blob/master/CONTRIBUTING.md) for details.
 
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