Add Source Serif 4 (#17)

Author: MDLC01

NOTICE

@@ -73,6 +73,10 @@ The SIL Open Font License Version 1.1 applies to:
   Copyright 2017 The Inria Sans Project Authors
   (https://github.com/BlackFoundryCom/InriaFonts)
 
+* Source Serif 4 fonts in files/fonts/SourceSerif4*.otf
+  Copyright 2014 - 2023 Adobe (http://www.adobe.com/),
+  with Reserved Font Name ‘Source’.
+
 * XITS fonts in files/fonts/XITS*.otf
   Copyright (c) 2001-2010, STI Pub Companies, consisting of the American
   Institute of Physics, the American Chemical Society, the American Mathematical
@@ -915,7 +919,7 @@ particular
 1. be copied, printed, presented, altered, processed and transmitted to third
 parties;
 2. be merged with own data and with the data of others and be combined to form
-new and independent datasets; 
+new and independent datasets;
 3. be integrated in internal and external business processes, products and
 applications in public and non-public electronic networks.
 
@@ -934,7 +938,7 @@ information 1-3 for the source note.
 (3) Changes, editing, new designs or other amendments must be marked as such in
 the source note.
 
- 
+
 
 URL: http://www.govdata.de/dl-de/by-2-0
 ================================================================================

files/fonts/SourceSerif4-Regular.otf

@@ -94,6 +94,7 @@ files! {
     "fonts/PTSans-Regular.ttf",
     "fonts/Roboto-Regular.ttf",
     "fonts/STIXTwoMath-Regular.otf",
+    "fonts/SourceSerif4-Regular.otf",
     "fonts/TwitterColorEmoji.ttf",
     "fonts/Ubuntu-Regular.ttf",
     "fonts/XITSMath-Regular.otf",