Update README.md

Author: eumel8

README.md

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 # carbon-app
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+A Golang app to display the `entsoe_generation_eco` metrik in a window. Works cross-plattformed on Linux, Windows, and Mac.
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+The app needs a Prometheus endpoint with the required metrik. See [caas-carbon-footprint](https://github.com/caas-team/caas-carbon-footprint) for more details.
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+Example showcase, desribed in this [blog post](https://blog.eumel.de/2024/06/19/raspberry-pi-carbon-app.html), [en](https://blog.eumel.de/2024/06/19/raspberry-pi-carbon-app-en.html)
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+<img src="https://blog.eumel.de/images/2024-06-19_1.jpg" width="585" height="386"/>