add third party license README

Author: chrissimpkins

thirdparty/README.md

@@ -0,0 +1,5 @@
+# Third Party Licenses
+
+The Slice project uses a subset derivative of the [Monoton typeface](https://fonts.google.com/specimen/Monoton) by Vernon Adams.  This software is used and distributed under the SIL Open Font License, Version 1.1. Please see [Monoton-OFL.txt](https://github.com/source-foundry/Slice/blob/main/thirdparty/Monoton-OFL.txt) for additional details.
+
+The Slice project uses the ["cheesecake" icon](https://www.flaticon.com/free-icon/cheesecake_3400263) released by flaticon.com.  This image is used and distributed under the [Flaticon license](https://github.com/source-foundry/Slice/blob/main/thirdparty/Flaticon-License.txt).  Please see Flaticon-License.txt for additional details.