Add Scanned Head 3D data asset

examples/textures/3d/Readme.txt

@@ -0,0 +1,9 @@
+** head256x256x109.zip
+
+This file is from
+
+https://www.codeproject.com/Articles/352270/Getting-started-with-Volume-Rendering
+
+This file is licensed under The Code Project Open License (CPOL)
+
+https://www.codeproject.com/info/cpol10.aspx