If you click into any incident you'll be brought to the Incident Details Page, where you can update and edit the different sections, as well as add comments. Full details on the different sections that can be updated can be found here.
If an overall quick update is needed for those working on or keeping tabs on the incident, you can add a Headline Status which will be visible in the Incident List page, as well as within the incident itself.
To add the overall comment, once you're in the incident, you'll see the Headline Status section in the details tab
By adding in a comment here, the text will be visible and bold once any user clicks into the incident
It will also show a Headline Status icon within the Incident List page. Once hovered over, any user can see the comment made to get a snapshot update on the incident