Add some explanation to Repository#update_branch_with_hooks

    fetch_ref(path_to_repo, ref, ref_path)

  end

  # Whenever `source_branch` is passed, if `branch` doesn't exist, it would

  # be created from `source_branch`.

  # Whenever `source_branch` or `source_commit` is passed, if `branch`

  # doesn't exist, it would be created from `source_branch` or

  # `source_commit`. Should only pass one of them, not both.

  # If `source_project` is passed, and the branch doesn't exist,

  # it would try to find the source from it instead of current repository.

  def update_branch_with_hooks(

    current_user, branch,

    source_branch: nil, source_commit: nil, source_project: project)