[DOC] update docs for new gt_ref_depths, gt_alt_depths, and gt_quals columns
[DOC] update docs for new gt_ref_depths, gt_alt_depths, and gt_quals columns

heuermh/gemini,heuermh/gemini,arq5x/gemini,arq5x/gemini,arq5x/gemini,xuzetan/gemini,udp3f/gemini,xuzetan/gemini,bw2/gemini,brentp/gemini,udp3f/gemini,xuzetan/gemini,bpow/gemini,bw2/gemini,udp3f/gemini,bgruening/gemini,bw2/gemini,bpow/gemini,heuermh/gemini,brentp/gemini,bpow/gemini,bgruening/gemini,heuermh/gemini,brentp/gemini,xuzetan/gemini,arq5x/gemini,bgruening/gemini,brentp/gemini,bw2/gemini,bgruening/gemini,bpow/gemini,udp3f/gemini