Examples: Add license for kenpixel.ttf. (#21778)

examples/fonts/ttf/README.md

@@ -0,0 +1,9 @@
+# Kenney Fonts
+
+## Source
+
+https://www.kenney.nl/assets/kenney-fonts
+
+## License
+
+CC0 1.0 Universal (CC0 1.0) Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/)