[network] Describe Grid5000 backbone

data/grid5000/network_equipments/renater5-bordeaux.json

data/grid5000/network_equipments/renater5-grenoble.json

data/grid5000/network_equipments/renater5-lille.json

data/grid5000/network_equipments/renater5-luxembourg.json

data/grid5000/network_equipments/renater5-lyon.json

data/grid5000/network_equipments/renater5-marseille.json

data/grid5000/network_equipments/renater5-nancy.json

data/grid5000/network_equipments/renater5-paris.json

data/grid5000/network_equipments/renater5-reims.json

data/grid5000/network_equipments/renater5-sophia.json

data/grid5000/network_equipments/renater5-toulouse.json