Copyedit license management docs

Achilleas Pipinellisrequested to merge
docs/license-management-copyedit into master

What does this MR do?

After some discussion in https://gitlab.slack.com/archives/C8S0HHM44/p1529661460000098, dependency manager should be package manager.

closes https://gitlab.com/gitlab-org/gitlab-ce/issues/47859

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