Update link on the Gutenberg build files notice (#15697)

gutenberg.php

@@ -89,7 +89,7 @@ function gutenberg_wordpress_version_notice() {
  */
 function gutenberg_build_files_notice() {
 	echo '<div class="error"><p>';
-	_e( 'Gutenberg development mode requires files to be built. Run <code>npm install</code> to install dependencies, <code>npm run build</code> to build the files or <code>npm run dev</code> to build the files and watch for changes. Read the <a href="/WordPress/gutenberg/blob/master/CONTRIBUTING.md">contributing</a> file for more information.', 'gutenberg' );
+	_e( 'Gutenberg development mode requires files to be built. Run <code>npm install</code> to install dependencies, <code>npm run build</code> to build the files or <code>npm run dev</code> to build the files and watch for changes. Read the <a href="/WordPress/gutenberg/blob/master/docs/contributors/getting-started.md">contributing</a> file for more information.', 'gutenberg' );
 	echo '</p></div>';
 }