Add package for Ubuntu 20.04

[minhduc0711]

It would be great if I can just apt install on 20.04. Thanks in advance!

[jordan-da]

...someone should put a bounty on this and I will pay

[vhdsih]

on ubuntu 20.04, run:
sudo apt install gobject-introspection;
sudo apt install gtk-doc-tools;
sudo apt install libjson-glib-dev；
then you can make the code.