modify the readme.md so that the sample xml configuration file can be viewed correctly on webpage

README.md

@@ -16,6 +16,7 @@ There is no vertex normal information included in ShapeNet dataset, so it would
 
 A sample rendering configuration render.xml:
 
+```xml
 <?xml version="1.0" encoding="utf-8"?>
 
 <scene version="0.5.0">
@@ -46,4 +47,5 @@ A sample rendering configuration render.xml:
 			<boolean name="banner" value="false"/>
 		</film>
 	</sensor>
-</scene>
\ No newline at end of file
+</scene>
+```
\ No newline at end of file