fix bad python-gitlab instructions
fix bad python-gitlab instructions

For installing prerequisites the python-gitlab doc was missing
the install command.

logicminds/gitlab-mirrors,samrocketman/gitlab-mirrors,logicminds/gitlab-mirrors,mahajanankur/gitlab-mirrors,sbellver/gitlab-mirrors,mahajanankur/gitlab-mirrors,samrocketman/gitlab-mirrors,sbellver/gitlab-mirrors