added a white background version of the unity logo and switched to it

README.md

-<img src="com.unity.perception/Documentation~/images/unity-wide.png" align="middle" width="3000"/>
+<img src="com.unity.perception/Documentation~/images/unity-wide-whiteback.png" align="middle" width="3000"/>
 
 <img src="com.unity.perception/Documentation~/images/banner2.PNG" align="middle"/>
 

com.unity.perception/Documentation~/Tutorial/TUTORIAL.md

-<img src="../images/unity-wide.png" align="middle" width="3000"/>
+<img src="../images/unity-wide-whiteback.png" align="middle" width="3000"/>
 
 # Perception Tutorial