Update README.md

Update README to indicate deprecated functionality and provide alternative link.

Author: jeffjennings

README.md

@@ -1,5 +1,5 @@
 **The functionality in this tutorial is deprecated.** 
 Please see [this alternative approach](https://irsa.ipac.caltech.edu/docs/vo_scs.html) to the workflow in the tutorial using PyVO. 
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 This directory contains tutorials related to `astroquery.vo_conesearch` package.