Downloads header definition update

[ljwh2]

https://www.ebi.ac.uk/gwas/docs/fileheaders#_file_headers_for_ancestry_download https://github.com/EBISPOT/gwas-ui/blob/documentation/goci-interfaces/goci-ui/src/main/docs/fileheaders-content.adoc

Action: update definition of “Broad ancestral category” New definition: BROAD ANCESTRAL CATEGORY: Ancestry category group label, assigned to reduce complexity within the data sets and place samples in context. For more information please refer to documentation [link]

Note, I haven't done this yet since we need the link