Fix dead link

Author: sebastianbergmann

README.md

@@ -19,7 +19,7 @@ $ php phpunit-X.Y.phar --version
 
 Please replace `X.Y` with the version of PHPUnit you are interested in.
 
-Alternatively, you may use [Composer](https://getcomposer.org/) to download and install PHPUnit as well as its dependencies. Please refer to the "[Getting Started](https://phpunit.de/getting-started-with-phpunit.html)" guide for details on how to install PHPUnit.
+Alternatively, you may use [Composer](https://getcomposer.org/) to download and install PHPUnit as well as its dependencies. Please refer to the [documentation](https://phpunit.de/documentation.html) for details on how to install PHPUnit.
 
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