Add file names in tests/data/README.md

diff --git a/tests/data/README.md b/tests/data/README.md
index 55b36dc..5d5228c 100644
--- a/tests/data/README.md
+++ b/tests/data/README.md
@@ -4,8 +4,14 @@
 
 ### Files `kodim*`
 
+#### File [kodim03_yuv420_8bpc.avif](io/kodim03_yuv420_8bpc.avif)
+
 ![](io/kodim03_yuv420_8bpc.avif)
 
+License: released by the Eastman Kodak Company for unrestricted usage
+
+#### File [kodim23_yuv420_8bpc.avif](io/kodim23_yuv420_8bpc.avif)
+
 ![](io/kodim23_yuv420_8bpc.avif)
 
 License: released by the Eastman Kodak Company for unrestricted usage
@@ -14,6 +20,8 @@
 
 ### Files `cosmos*`
 
+#### File [cosmos1650_yuv444_10bpc_p3pq.avif](io/cosmos1650_yuv444_10bpc_p3pq.avif)
+
 ![](io/cosmos1650_yuv444_10bpc_p3pq.avif)
 
 License: [Creative Commons Attribution license (reuse allowed)](https://creativecommons.org/licenses/by/3.0/legalcode)