Update gitlab admin user and password info

The information about admin user and password for a new gitlab installation was outdated, I have changed the information to reflect changes in the self hosted version of Gitlab.

book/04-git-server/sections/gitlab.asc

@@ -24,8 +24,7 @@ For more information read the https://gitlab.com/gitlab-org/gitlab-foss/-/blob/m
 ==== Administration
 
 GitLab's administration interface is accessed over the web.
-Simply point your browser to the hostname or IP address where GitLab is installed, and log in as the admin user.
-The default username is `[email protected]`, and the default password is `5iveL!fe` (which you must change right away).
+Simply point your browser to the hostname or IP address where GitLab is installed, and log in as the `root` user. The password will depend on your installation type but by default, Omnibus GitLab automatically generates a password for and stores it to /etc/gitlab/initial_root_password for at least 24 hours. Follow the documentation for more details.
 After you've logged in, click the "`Admin area`" icon in the menu at the top right.
 
 [[gitlab_menu]]