Fix URLs in chapter 13 of Admin Guide (#1186)

Author: sspencerwire

docs/books/admin_guide/13-softwares.md

@@ -926,7 +926,7 @@ Examples:
 * Download a `.repo` file and use it:
 
 ```
-dnf config-manager --add-repo https://packages._centreon_.com/rpm-standard/23.04/el8/_centreon_.repo
+dnf config-manager --add-repo https://packages.centreon.com/ui/native/rpm-standard/23.04/el8/centreon-23.04.repo
 ```
 
 * You can also set an url as a base url for a repo: