update citation in docs

Author: nspope

docs/citation.md

@@ -18,16 +18,17 @@ kernelspec:
 
 # Citation
 
-The algorithm for the `inside_outside` and `maximization` methods is described
+The default `variational_gamma` method is described in a
+[preprint](https://www.biorxiv.org/content/10.64898/2026.01.07.698223v1), and
+should be cited by published work using tsdate versions 0.2 or higher:
+
+> Nathaniel S. Pope, Sam Tallman, Ben Jeffery, Duncan Robertson, Yan Wong, Savita Karthikeyan, Peter L. Ralph, and Jerome Kelleher (2026) _Tracing the evolutionary histories of ultra-rare variants using variational dating of large ancestral recombination graphs_. bioRxiv: 2026.01.07.698223; doi: https://doi.org/10.64898/2026.01.07.698223
+
+The algorithm for the `inside_outside` and `maximization` methods (the defaults
+prior to version 0.2) is described
 in [our Science paper](https://www.science.org/doi/10.1126/science.abi8264) (citation below,
 preprint [here](https://www.biorxiv.org/content/10.1101/2021.02.16.431497v2)).
 [Another repository](https://github.com/awohns/unified_genealogy_paper) provides
 code to reproduce evaluations of the accuracy and computational requirements of these methods.
-The default `variational_gamma` method has not yet been described in print. For the moment,
-please cite this github repository if you need a citable reference.
-
-The original _tsdate_ algorithm, which you should cite in published work, is published in:
 
 > Anthony Wilder Wohns, Yan Wong, Ben Jeffery, Ali Akbari, Swapan Mallick, Ron Pinhasi, Nick Patterson, David Reich, Jerome Kelleher, and Gil McVean (2022) *A unified genealogy of modern and ancient genomes*. Science **375**: eabi8264; doi: https://doi.org/10.1126/science.abi8264
-
-