improve documentation: annotate_variants_keytable (#1379)
improve documentation: annotate_variants_keytable (#1379)

* improve documentation: annotate_variants_keytable

* Update dataset.py

danking/hail,hail-is/hail,cseed/hail,danking/hail,hail-is/hail,hail-is/hail,cseed/hail,danking/hail,cseed/hail,cseed/hail,danking/hail,cseed/hail,cseed/hail,hail-is/hail,hail-is/hail,hail-is/hail,danking/hail,danking/hail,cseed/hail,hail-is/hail,hail-is/hail,cseed/hail,danking/hail,danking/hail