Add carbon-fr to Carbon Awareness — French grid carbon intensity API

Adds carbon-fr to the Carbon Awareness section.

carbon-fr is an open-source API that serves the carbon intensity (gCO₂eq/kWh) of the French electricity grid, at national level and for the 12 metropolitan regions, built on RTE/éCO2mix open data (via ODRÉ).

Several tools already in this section — Carbon-minimiser, Grid-intensity-go — rely on the UK National Grid carbon intensity API to decide when and where to run jobs. carbon-fr brings the equivalent open data source for France, and goes further on two points:

- it adds historical series and an up-to-72h forecast that the source data doesn't provide;
- it exposes carbon-aware scheduling endpoints that surface the greenest upcoming window to shift compute.

Open source (MIT OR Apache-2.0) and self-hostable, with no API key or quota for consumers.

Author: morgan-voltz

README.md

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+- [carbon-fr](https://github.com/Kovelt/carbon-fr): Open API for the carbon intensity (gCO₂eq/kWh) of the French electricity grid, national and per-region, built on RTE/éCO2mix open data. Adds historical series and an up-to-72h forecast absent from the source, plus carbon-aware scheduling endpoints that surface the greenest upcoming window to shift compute. Self-hostable, MIT OR Apache-2.0.
 
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 ### Contributing to GitHub's Green Software Directory