Tweaked README.md

README.md

@@ -8,11 +8,11 @@ Usage:
 
 where
 
-   - velocity_1 is the velocity of the first particle, in the form
+   - ```velocity_1``` is the velocity of the first particle, in the form
      ```"r theta"``` if the input vector type is polar, or in the
      form ```"x y"``` if the input vector type is cartesian
 
-   - velocity_2 is the velocity of the second particle, in the
+   - ```velocity_2``` is the velocity of the second particle, in the
      form ```"r theta"``` if the input vector type is polar, or in
      the form ```"x y"``` if the input vector type is cartesian