Fix README

Author: eborghi10

Diff for: ca_description/README.md

@@ -15,7 +15,7 @@ To convert the xacro file into a URDF file:
 ```bash
 $ roscd ca_description/urdf/
 $ roscore &
-$ rosrun xacro xacro --inorder create_2.xacro [ARGS] > test.urdf
+$ rosrun xacro xacro --inorder create_2.urdf.xacro [ARGS] > test.urdf
 ```
 Replace [ARGS] with the corresponding XACRO arguments. As an example, `visualize:=false`.