Fix typos in OKR
Makes a few typos on https://about.gitlab.com/okrs/:
- a relative link (!6491 (merged))
- a wrong markdown for a link
- a wrong markdown for a nested list
Edited by username-removed-100770
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Makes a few typos on https://about.gitlab.com/okrs/: