Install unity-scope-devhelp by entering the following commands in the terminal:
sudo apt update sudo apt install unity-scope-devhelp
Description:
devhelp scope for Unity
This package contains the "devhelp" scope which allows Unity to search for devhelp content.
Homepage: https://launchpad.net/unity-scope-devhelp
Version: 0.1+14.04.20140328-0ubuntu3
Section: universe/gnome