DOC: distutils: Add a docstring to show_config().

Thanks to Sergey Kojoian for the original patch to create
the docstring.

Closes numpygh-9258.

doc/source/reference/routines.other.rst

@@ -44,6 +44,7 @@ Utility
    :toctree: generated/
 
    get_include
+   show_config
    deprecate
    deprecate_with_doc
 

numpy/distutils/misc_util.py

@@ -2326,6 +2326,43 @@ def get_info(name):
                 return g.get(name, g.get(name + "_info", {}))
 
             def show():
+                """
+                Show libraries in the system on which NumPy was built.
+
+                Print information about various resources (libraries, library
+                directories, include directories, etc.) in the system on which
+                NumPy was built.
+
+                See Also
+                --------
+                get_include : Returns the directory containing NumPy C
+                              header files.
+
+                Notes
+                -----
+                Classes specifying the information to be printed are defined
+                in the `numpy.distutils.system_info` module.
+
+                Information may include:
+
+                * ``language``: language used to write the libraries (mostly
+                  C or f77)
+                * ``libraries``: names of libraries found in the system
+                * ``library_dirs``: directories containing the libraries
+                * ``include_dirs``: directories containing library header files
+                * ``src_dirs``: directories containing library source files
+                * ``define_macros``: preprocessor macros used by
+                  ``distutils.setup``
+
+                Examples
+                --------
+                >>> np.show_config()
+                blas_opt_info:
+                    language = c
+                    define_macros = [('HAVE_CBLAS', None)]
+                    libraries = ['openblas', 'openblas']
+                    library_dirs = ['/usr/local/lib']
+                """
                 for name,info_dict in globals().items():
                     if name[0] == "_" or type(info_dict) is not type({}): continue
                     print(name + ":")