Add README.

ndtypes/README.rst

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+Overview
+--------
+
+The ``ndtypes`` module is the Python interface to the ``libndtypes`` library.
+``libndtypes`` implements dynamic types relevant for scientific computing.
+
+These types contain full memory layout information and are used both for type
+checking and  accessing values in memory.
+
+Types are specified using a close variant of the datashape language.
+
+``ndtypes`` supports other container modules.  It displays types, performs
+type checking, and the concrete type layout information is used to traverse
+memory.
+
+As an example, ``xnd`` is a container module that is based on ``ndtypes``.
+
+Links
+-----
+
+* https://github.com/xnd-project/