changed venus' texture to an almost white one

LICENSE.md

@@ -5,7 +5,9 @@
 - 3D models: Original art, placed under the Creative Commons CC0 License
 - Photographs of celestial bodies:
     - Mercury: [By Solar System Scope, CC BY 4.0](https://www.solarsystemscope.com/textures/)
-    - Venus: [By NASA, public domain](https://space.jpl.nasa.gov/tmaps/venus.html)
+    - Venus: [By Björn Jónsson, free to use, with attribution](https://bjj.mmedia.is/data/venus/venus.html)
+        - To reduce the visibility of the ultraviolet features in Björn's original image, I applied GIMP's "Colors"→"Hue-Saturation" with Lightness=100 and Saturation=-20.
+        - Exported as 80% quality JPEG
     - Earth: A simple addition of
         - [base image, by NASA, public domain](https://visibleearth.nasa.gov/images/74318/april-blue-marble-next-generation-w-topography)
         - [clouds, by NASA, public domain](https://visibleearth.nasa.gov/images/57747/blue-marble-clouds)