Update README.md

note about numba relase

README.md

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 # Single-cell Hierarchical Poisson Factorization
 
+## Update
+A newer version of the code, which uses numba and is substantially more computationally effiecient is available on branch rewrite_release.  It will be merged into master shortly.
+
+## About
 Pre-release of [Single-cell Hierarchical Poisson Factorization (scHPF)](https://www.biorxiv.org/content/early/2018/07/11/367003), as described in the forthcoming manuscript: <br/> *De novo* Gene Signature Identification from Single-Cell RNA-Seq with Hierarchical Poisson Factorization.
 
 scHPF is a tool for _de novo_ discovery of both discrete and continuous expression patterns in single-cell RNA\-sequencing (scRNA-seq) data. It adapts [Hierarchical Poisson Factorization](http://www.cs.columbia.edu/~blei/papers/GopalanHofmanBlei2015.pdf) to avoid prior normalization and model variable sparsity across genes and cells. Algorithmic details, benchmarking against alternative methods, and scHPF's application to a spatially sampled high-grade glioma can be found in our [paper on biorXiv](https://www.biorxiv.org/content/early/2018/07/11/367003).