DOC: Gallery example "Highlight country, continent and state polygons" - add details on country code (#4002)

Author: yvonnefroehlich

examples/gallery/maps/country_polygons.py

@@ -2,11 +2,12 @@
 Highlight country, continent and state polygons
 ===============================================
 
-The :meth:`pygmt.Figure.coast` method can highlight country polygons
-via the ``dcw`` parameter. It accepts the country code or full
-country name and can draw its borders and add a color to its landmass.
-It's also possible to define multiple countries at once by separating
-the individual names with commas.
+The :meth:`pygmt.Figure.coast` method can highlight country polygons via the ``dcw``
+parameter. It accepts the country code (following the 2-letter
+`ISO 3166-1 alpha-2 convention <https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2>`_) or
+full country name and can draw its borders and add a color to its landmass. It's also
+possible to define multiple countries at once by separating the individual names with
+commas.
 """
 
 # %%

pygmt/src/coast.py

@@ -168,7 +168,7 @@ def coast(
         *code1,code2,…*\ [**+g**\ *fill*\ ][**+p**\ *pen*\ ][**+z**].
         Select painting country polygons from the `Digital Chart of the World
         <https://en.wikipedia.org/wiki/Digital_Chart_of_the_World>`__.
-        Append one or more comma-separated countries using the 2-character
+        Append one or more comma-separated countries using the 2-letter
         `ISO 3166-1 alpha-2 convention
         <https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2>`__.
         To select a state of a country (if available), append .\ *state*,