Update README.md

Author: icweaver

README.md

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+[![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://juliaastro.org/Astroalign.jl/dev)
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 An experimental reimplementation of [astroalign](https://github.com/quatrope/astroalign) in Julia.
 
 Credit: [_Beroiz, M., Cabral, J. B., & Sanchez, B. (2020)_](https://ui.adsabs.harvard.edu/abs/2020A%26C....3200384B/abstract)
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-Documentation: https://juliaastro.org/Astroalign.jl/notebook.html