Add placeholder for missing fields in vario.md (OBOFoundry#2374)

* Add placeholder for missing fields in vario.md
* Add suggested changes

Author: deepakunni3

ontology/vario.md

@@ -29,5 +29,7 @@ publications:
   title: 'Variation ontology: annotator guide'
 - id: https://www.ncbi.nlm.nih.gov/pubmed/25616435
   title: Types and effects of protein variations
+repository: N/A
+tracker: http://variationontology.org/instructions.shtml
 activity_status: orphaned
 ---