update snakemake readme (#1788)

Author: fneum

README.md

@@ -105,7 +105,7 @@ SPDX-License-Identifier: CC-BY-4.0
 ![Size](https://img.shields.io/github/repo-size/pypsa/pypsa-eur)
 [![Zenodo PyPSA-Eur](https://zenodo.org/badge/DOI/10.5281/zenodo.3520874.svg)](https://doi.org/10.5281/zenodo.3520874)
 [![Zenodo PyPSA-Eur-Sec](https://zenodo.org/badge/DOI/10.5281/zenodo.3938042.svg)](https://doi.org/10.5281/zenodo.3938042)
-[![Snakemake](https://img.shields.io/badge/snakemake-≥8.14.0-brightgreen.svg?style=flat)](https://snakemake.readthedocs.io)
+[![Snakemake](https://img.shields.io/badge/snakemake-≥9-brightgreen.svg?style=flat)](https://snakemake.readthedocs.io)
 [![Discord](https://img.shields.io/discord/911692131440148490?logo=discord)](https://discord.gg/AnuJBk23FU)
 [![REUSE status](https://api.reuse.software/badge/github.com/pypsa/pypsa-eur)](https://api.reuse.software/info/github.com/pypsa/pypsa-eur)