Make link to published version more prominent

Author: mwcraig

README.md

@@ -5,7 +5,7 @@ The inspiration for this work is two guides and a book:
 + [A User's Guide to Stellar CCD Photometry with IRAF](https://www.mn.uio.no/astro/english/services/it/help/visualization/iraf/daophot2.pdf) Massey and Davis (1992)
 + [A User's Guide to CCD Reductions with IRAF](http://ircamera.as.arizona.edu/Astr_518/irafguid.pdf) Massey (1997)
 
-# Web version of the guide
+# [Latest published version](http://www.astropy.org/ccd-reduction-and-photometry-guide/) of the guide
 
 The rendered version of the guide is [here](http://www.astropy.org/ccd-reduction-and-photometry-guide/).