docs: fix comment referencing secrets to create

[carlsonp]

Checklist

• [X] The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• [X] Links to related issues (if applicable)
• [X] Tests for the changes have been added/updated (if applicable)
• [X] Docs related to the changes have been added/updated (if applicable)

This small change fixes a likely typo referencing the wrong secret name (extra "n") and cleans it up with commas.