Update README.md

Author: katilp

README.md

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 # 2010-minimumbias-trackvertex
 Validation code for 2010 MinimumBias dataset, based on track and vertex spectra
 
+It is based on the original code in [http://opendata.cern.ch/record/462] on the CERN Open Data portal (Geiser, Achim; Dutta, Irene; Hirvonsalo, Harri; Sheeran, Bridget; (2016). Validation code for 2010 MinimumBias dataset, based on track and vertex spectra. CERN Open Data Portal. DOI:10.7483/OPENDATA.CMS.GBZR.7F2A ) and modified here for direct download from github.
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 You need to work in a Virtual Machine properly contextualized for CMS. Everything is available on the CERN Open Data Portal:
 http://opendata.cern.ch/VM/CMS/2010.