There are two recommended options that you can use this for.
We have a keyword feature available for Docs, where you can enter in specific terms that will then be associated with that Doc. So when they next search for it, the Doc will also be displayed.
The Keywords tab is available when editing/creating a Docs page.
Having these searches available, might help you identify areas where new Docs are needed. So if you see that users are continuously searching a specific word/question, it might be time to create a new Doc based upon this.