Add badges

Author: mstimberg

README.md

@@ -1,2 +1,6 @@
 # QuantSI
+[![Ruff](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/astral-sh/ruff/main/assets/badge/v2.json)](https://github.com/astral-sh/ruff)
+[![Tests](https://github.com/brian-team/QuantSI/actions/workflows/pytest-ubuntu.yaml/badge.svg)](https://github.com/brian-team/QuantSI/actions/workflows/pytest-ubuntu.yaml)
+[![Coverage Status](https://coveralls.io/repos/github/brian-team/QuantSI/badge.svg?branch=main)](https://coveralls.io/github/brian-team/QuantSI?branch=main)
+
 Work in progress: unit system as used by the Brian2 simulator