Document common aliases for grdimage

Add automatic docstrings for frame (B), cmap (C), projection (J), region (R), timestamp (U), verbose (V), and interpolation (n). Also removed alias pen (W) that  actually doesn't work.

Author: weiji14

pygmt/base_plotting.py

@@ -303,12 +303,14 @@ def grdcontour(self, grid, **kwargs):
 
     @fmt_docstring
     @use_alias(
-        R="region",
-        J="projection",
-        W="pen",
         B="frame",
-        I="shading",
         C="cmap",
+        I="shading",
+        J="projection",
+        R="region",
+        U="timestamp",
+        V="verbose",
+        n="interpolation",
         t="transparency",
     )
     @kwargs_to_strings(R="sequence")
@@ -326,6 +328,12 @@ def grdimage(self, grid, **kwargs):
         ----------
         grid : str or xarray.DataArray
             The file name of the input grid or the grid loaded as a DataArray.
+        {B}
+        {CPT}
+        {J}
+        {R}
+        {V}
+        {n}
         {t}
 
         """