Update gmt2kml.rst

doc/rst/source/gmt2kml.rst

@@ -87,7 +87,7 @@ Optional Arguments
     altitude, **g** altitude relative to the ground, or **s**
     altitude relative to seafloor. To plot the features at a
     fixed altitude, append an altitude *alt* (in m). Use 0 to clamp the
-    features to the chosen reference surface. Append **x**\ *scale* to
+    features to the chosen reference surface. Alternatively, append **x**\ *scale* to
     scale the altitude from the input file by that factor. If no value
     is appended, the altitude (in m) is read from the 3rd column of the
     input file. [By default the features are clamped to the sea surface or ground].