added doc status

Author: jtschindler

README.md

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 # SpecOneD
 
+[![Documentation Status](https://readthedocs.org/projects/speconed/badge/?version=latest)](https://speconed.readthedocs.io/en/latest/?badge=latest)
+
 SpecOneD is a lightweight python package that introduces the SpecOneD class for the manipulation of one-dimensional astronomical spectra.
 
 For installation instructions and documentation visit [SpecOneD's ReadTheDocs]