Install grass-doc by entering the following commands in the terminal:
sudo apt update sudo apt install grass-doc
Description:
GRASS GIS user documentation
Commonly referred to as GRASS, this is a Geographic Information System (GIS) used for geospatial data management and analysis, image processing, graphics/map production, spatial modeling, and visualization. GRASS is currently used in academic and commercial settings around the world, as well as by many government agencies and environmental consulting companies. . This package contains HTML documentation for the GRASS system.
Homepage: http://grass.osgeo.org/
Version: 7.4.0-1
Section: universe/science