Update README.md

Author: nhz2

README.md

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 # SimplexCellLists WIP
 
 [![Build Status](https://github.com/medyan-dev/SimplexCellLists.jl/actions/workflows/CI.yml/badge.svg?branch=main)](https://github.com/medyan-dev/SimplexCellLists.jl/actions/workflows/CI.yml?query=branch%3Amain)
+![Julia Support](https://img.shields.io/badge/Julia-1.8-blue)
 
 This Julia package accelerates computations on all pairs of 3D points, line segments, and triangles within a cutoff distance.