[README.md] update acknowledgments

Author: chrissimpkins

README.md

@@ -37,6 +37,8 @@ Please see the [thirdparty directory](https://github.com/source-foundry/Slice/tr
 
 ❤️ Slice slices with the fantastic [fonttools Python library](https://github.com/fonttools/fonttools).
 
+❤️ Slice uses the wonderful [Recursive](https://github.com/arrowtype/recursive) (sliced with Slice!) and [IBM Plex](https://github.com/IBM/plex) typefaces in the UI.
+
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