Hello Raphael,
You can SSH into your Edison and execute the following commands shown below in bold:
echo"src mraa-upm http://iotdk.intel.com/repos/1.1/intelgalactic"> /etc/opkg/mraa-upm.conf
opkg update
opkg install libmraa0
The MRAA github page is here: https://github.com/intel-iot-devkit/mraa
You can find more information on the github page.
I hope this helps.
Regards,
Nischal