That definitely is in the documentation. It's a little easy to miss, especially if you didn't actually do the walkthrough and simply read it.
Check this section of the full walkthrough.
This is a Directive. Directives are special events that display a message on the HUD telling you what to do. They are frequently confused with Objectives (also known as Goals) which if you remember, we filled in earlier using the Mission Objectives Editor. When the event comes true, a directive will be marked on the HUD as completed. If it is impossible to complete a directive, it will turn red. To make this event into a directive you simply need to fill in the Directive Text. Type Combat Landing Authorised into that box and the event will turn red, indicating that it is a directive. We also want it chained (with a Chain Delay of 0).
Basically you just fill in the Directive Text and an event becomes a Directive.