$ sudo apt-get update
$ sudo apt-get install musescore-soundfont-gm 

musescore-soundfont-gm is installed in your system.

Make ensure the musescore-soundfont-gm package were installed using the commands given below,

$ sudo dpkg-query -l | grep musescore-soundfont-gm *

You will get with musescore-soundfont-gm package name, version, architecture and description in a table

musescore-soundfont-gm package basic information: