add alevin-fry reference

content/02.introduction.md

@@ -25,7 +25,7 @@ All data provided on the portal are available in formats ready for downstream an
 
 To ensure that all current and future data on the Portal are uniformly processed, we created scpca-nf, a Nextflow-based open-source pipeline (https://github.com/AlexsLemonade/scpca-nf).
 Using a consistent pipeline for all data increases transparency and allows users to perform analysis across multiple samples and projects without having to do any re-processing.
-The scpca-nf workflow uses alevin-fry for fast and efficient quantification of gene expression for all samples on the Portal, including single-cell RNA-seq data and any associated ADT/CITE-seq or cell hash data, spatial transcriptomics data, and bulk RNA-seq data.
+The scpca-nf workflow uses alevin-fry [@doi:10.1038/s41592-022-01408-3] for fast and efficient quantification of gene expression for all samples on the Portal, including single-cell RNA-seq data and any associated ADT/CITE-seq or cell hash data, spatial transcriptomics data, and bulk RNA-seq data.
 The scpca-nf pipeline also serves as a resource for the community, allowing others to process their own samples for comparison to samples available on the Portal and allowing us to accept uniformly processed community contributions.
 
 Here, we present the Single-cell Pediatric Cancer Atlas as a resource for all pediatric cancer researchers.