link to new repo location of fuel-docs

astute links to the old repository location of fuel-docs:

    [root@fuel ~]# astute 
    CLI interface in Astute no longer supported. Please use new Fuel-CLI. 
    More details you can get by link: https://github.com/Mirantis/fuel-docs/blob/master/pages/user-guide/cli.rst

This pull request corrects this and makes it refer to the stackforge location