Added PBR related assets & Mutant credit information to the credits page.

Docs/Urho3D.dox

@@ -204,7 +204,11 @@ Jack and mushroom models from the realXtend project. (https://www.realxtend.org)
 Ninja model and terrain, water, smoke, flare and status bar textures from OGRE.<br>
 BlueHighway font from Larabie Fonts.<br>
 Anonymous Pro font by Mark Simonson.<br>
-NinjaSnowWar sounds by Veli-Pekka T&auml;til&auml;.
+NinjaSnowWar sounds by Veli-Pekka T&auml;til&auml;.<br>
+PBR textures from Substance Share. (https://share.allegorithmic.com)<br>
+IBL textures from HDRLab's sIBL Archive.<br>
+Dieselpunk Moto model by allexandr007.<br>
+Mutant model from Mixamo.<br>
 
 
 \page License License