Rename README to README.md and update it.

[skip ci]

README

-See INSTALL for installation instruction.

README.md

+dynamic-graph-python
+====================
+
+[![Build Status](https://travis-ci.org/stack-of-tasks/dynamic-graph-python.png?branch=master)](https://travis-ci.org/stack-of-tasks/dynamic-graph-python)
+[![Coverage Status](https://coveralls.io/repos/stack-of-tasks/dynamic-graph-python/badge.png)](https://coveralls.io/r/stack-of-tasks/dynamic-graph-python)
+
+Python bindings for dynamic-graph.
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