Default Font Source Sans 3 is not included

Problem/Motivation

As the title says, Source Sans 3 is configured in the Bootstrap variable. However, the font is not available.

https://fonts.google.com/specimen/Source+Sans+3
https://fonts.google.com/specimen/Source+Sans+3/license

I am not sure if the theme is allowed to add the font directly (by licence). Would it be a good idea to recommend using something like https://www.drupal.org/project/fontyourface?

Should be okay, just add:

This theme includes the following fonts licensed under the SIL Open Font License (OFL):

- Source Sans 3, Designed by Paul D. Hunt (https://fonts.google.com/specimen/Source+Sans+3)
Copyright 2010, 2012, 2014, 2017, 2019 Adobe Systems Incorporated (http://www.adobe.com/), with Reserved Font Name Source.
License: OFL (see OFL.txt or https://scripts.sil.org/OFL)

Required weights:
- 300
- 400
- 700

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes