Add Slack, YouTube and code style badge and remove Coveralls

Author: efaulhaber

README.md

@@ -2,7 +2,9 @@
 
 [![Docs-stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://trixi-framework.github.io/TrixiNeighborhoodSearch.jl/stable)
 [![Docs-dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://trixi-framework.github.io/TrixiNeighborhoodSearch.jl/dev)
+[![Slack](https://img.shields.io/badge/chat-slack-e01e5a)](https://join.slack.com/t/trixi-framework/shared_invite/zt-sgkc6ppw-6OXJqZAD5SPjBYqLd8MU~g)
+[![Youtube](https://img.shields.io/youtube/channel/views/UCpd92vU2HjjTPup-AIN0pkg?style=social)](https://www.youtube.com/@trixi-framework)
 [![Build Status](https://github.com/trixi-framework/TrixiNeighborhoodSearch.jl/workflows/CI/badge.svg)](https://github.com/trixi-framework/TrixiNeighborhoodSearch.jl/actions?query=workflow%3ACI)
-[![Coveralls](https://coveralls.io/repos/github/trixi-framework/TrixiNeighborhoodSearch.jl/badge.svg)](https://coveralls.io/github/trixi-framework/TrixiNeighborhoodSearch.jl)
 [![Codecov](https://codecov.io/gh/trixi-framework/TrixiNeighborhoodSearch.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/trixi-framework/TrixiNeighborhoodSearch.jl)
+[![SciML Code Style](https://img.shields.io/static/v1?label=code%20style&message=SciML&color=9558b2&labelColor=389826)](https://github.com/SciML/SciMLStyle)
 [![License: MIT](https://img.shields.io/badge/License-MIT-success.svg)](https://opensource.org/license/mit/)