Update docstring in borders gallery example (#1093)

Author: michaelgrund

examples/gallery/maps/borders.py

@@ -11,9 +11,9 @@
 * **3** = Marine boundaries
 * **a** = All boundaries (1-3)
 
-For example, to draw national boundaries with 1p thickness black lines use
-``borders="1/1p,black"``. You can draw multiple boundaries by passing in a list to
-``borders``.
+For example, to draw national boundaries with a line thickness of 1p and black line 
+color use ``borders="1/1p,black"``. You can draw multiple boundaries by passing in 
+a list to ``borders``.
 """
 import pygmt