update third party README with IBM Plex Mono license

Author: chrissimpkins

thirdparty/README.md

@@ -2,5 +2,6 @@
 
 The Slice project uses and distributes a derivative of 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.  Please see [Flaticon-License.txt](https://github.com/source-foundry/Slice/blob/main/thirdparty/Flaticon-License.txt) for additional details.
 
-
 The Slice project uses and distributes subset derivatives of the [Recursive typeface](https://github.com/arrowtype/recursive) by Stephen Nixon as test fonts and in the application UI. The software is used and distributed under the SIL Open Font License, Version 1.1. Please see [Recursive-OFL.txt](https://github.com/source-foundry/Slice/blob/main/thirdparty/Recursive-OFL.txt) for additional details.
+
+The Slice project uses and distributes the [IBM Plex Mono typeface](https://github.com/arrowtype/recursive) by IBM in the application UI. The software is used and distributed under the SIL Open Font License, Version 1.1. Please see [IBMPlex-OFL.txt](https://github.com/source-foundry/Slice/blob/main/thirdparty/IBMPlex-OFL.txt) for additional details.