Add PointSize doc example

Author: rocky

mathics/builtin/graphics.py

@@ -1001,6 +1001,9 @@ class PointSize(_Size):
     <dt>'PointSize[$t$]'
         <dd>sets the diameter of points to $t$, which is relative to the overall width.
     </dl>
+
+    >> Table[Graphics[{PointSize[r], Point[{0, 0}]}], {r, {0.02, 0.05, 0.1, 0.3}}]
+     = {-Graphics-, -Graphics-, -Graphics-, -Graphics-}
     """
 
     def get_size(self):