Add bibliographic reference to upstream metadata.

debian/upstream/metadata

+Reference:
+ - Author: Olivier Langella and Benoît Valot and Thierry Balliau and Mélisande Blein-Nicolas and Ludovic Bonhomme and Michel Zivy
+   Title: >
+    X!TandemPipeline: A Tool to Manage Sequence Redundancy for 
+    Protein Inference and Phosphosite Identification
+   Journal: Journal of Proteome Research
+   Year: 2017
+   Month: 2
+   Day: 3
+   Volume: 16
+   Number: 2
+   Pages: 494-503
+   DOI:  10.1021/acs.jproteome.6b00632
+   PMID: 27990826
+   URL: https://pubs.acs.org/doi/10.1021/acs.jproteome.6b00632
+   ePrint: https://pubs.acs.org/doi/pdf/10.1021/acs.jproteome.6b00632
+Repository : https://forgemia.inra.fr/pappso/xtpcpp