Small changes to PyData reference in README (#926)

Author: liamtoney

README.rst

@@ -86,8 +86,9 @@ Project goals
 * Build a Pythonic API for GMT.
 * Interface with the GMT C API directly using ctypes (no system calls).
 * Support for rich display in the Jupyter notebook.
-* Integration with the PyData Ecosystem: numpy.ndarray or pandas.DataFrame for data tables
-  and xarray.DataArray for grids.
+* Integration with the `PyData <https://pydata.org/>`__ ecosystem: 
+  ``numpy.ndarray`` or ``pandas.DataFrame`` for data tables and 
+  ``xarray.DataArray`` for grids.
 
 
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