Add runic badge to Readme

Author: jpthiele

README.md

@@ -6,6 +6,7 @@ VoronoiFVM.jl
 [![](https://img.shields.io/badge/docs-dev-blue.svg)](https://WIAS-PDELib.github.io/VoronoiFVM.jl/dev)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3529808.svg)](https://doi.org/10.5281/zenodo.3529808)
 [![Zulip Chat](https://img.shields.io/badge/zulip-join_chat-brightgreen.svg)](https://julialang.zulipchat.com/#narrow/stream/379007-voronoifvm.2Ejl)
+[![code style: runic](https://img.shields.io/badge/code_style-%E1%9A%B1%E1%9A%A2%E1%9A%BE%E1%9B%81%E1%9A%B2-black)](https://github.com/fredrikekre/Runic.jl)
 
 Solver for coupled nonlinear partial differential equations (elliptic-parabolic conservation laws) based on the Voronoi finite volume method.
 It uses automatic differentiation via [ForwardDiff.jl](https://github.com/JuliaDiff/ForwardDiff.jl) and [DiffResults.jl](https://github.com/JuliaDiff/DiffResults.jl) to evaluate user functions along with their jacobians and calculate derivatives of solutions with respect to their parameters.