Simple Docs generated asset licenses

Simple Docs code and the terminal and paper themes are licensed under the MIT
License in Simple-Docs-MIT.txt.

The Ef and Modus theme adaptations are licensed under GPL-3.0-or-later. Their
selected theme directory contains a NOTICE with exact authorship, copyright,
source revision, and modification information. The full license is in
GPL-3.0-or-later.txt.

JetBrains Mono is licensed under the SIL Open Font License 1.1. Its license is
in ../fonts/OFL.txt.
