[docs] update changelog command

[gallettilance]

Description of the change:

From the github_changelog_generator CLI help

Usage: github_changelog_generator --user USER --project PROJECT [options]
    -u, --user USER                  Username of the owner of target GitHub repo.
    -p, --project PROJECT            Name of project on GitHub.
    -t, --token [TOKEN]              To make more than 50 requests per hour your GitHub token is required. You can generate it at: https://github.com/settings/tokens/new
    -f, --date-format FORMAT         Date format. Default is %Y-%m-%d.
    -o, --output [NAME]              Output file. To print to STDOUT instead, use blank as path. Default is CHANGELOG.md
    -b, --base [NAME]                Optional base file to append generated changes to.
        --summary-label [LABEL]      Set up custom label for the release summary section. Default is "".
        --breaking-label [LABEL]     Set up custom label for the breaking changes section. Default is 

[jpeeler]

/lgtm
Thanks for the update

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gallettilance, jpeeler

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[gallettilance]

/test e2e-aws-console-olm

[gallettilance]

/test e2e-aws-olm

[gallettilance]

/test e2e-gcp