Update credits

Author: drfiemost

AUTHORS.md

@@ -23,6 +23,11 @@ supplied contributions or code was derived from their work:
     Thibaut VARENE    - exSID support
     LouD              - USBSID-Pico support
 
+3rd party libraries:
+
+    David Reid        - miniaudio
+    Victor Zverovich  - fmt
+    Steffen Schümann  - filesystem
 
 Credit where credit is due, so if I missed anyone please let me know.
 

README.md

@@ -82,6 +82,10 @@ the character conversion requires presence of the POSIX/XSI iconv function famil
   https://github.com/mackron/miniaudio
   distributed under MIT license
 
+* fmt
+  https://github.com/fmtlib/fmt
+  distributed under MIT license
+
 * filesystem
   https://github.com/gulrak/filesystem
   distributed under MIT license