Update README.rst

I have found those lines at the top of vim_ipython.py instead of ipy.vim

Author: arnaldorusso

README.rst

@@ -153,7 +153,7 @@ not work on Windows, please report the issue to ).
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 Options
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-You can change these at the top of the ipy.vim::
+You can change these at the top of the vim_ipython.py::
 
   reselect = False            # reselect lines after sending from Visual mode
   show_execution_count = True # wait to get numbers for In[43]: feedback?