docs(changelog): French transit networks (#1716)

changelog.d/1716-transit-french-networks.md

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+- Add 112 French networks to the Transit layer, from Nice, Dijon, Angers,
+  Brest, Le Mans, Metz, Amiens, Avignon and Valenciennes to small-town
+  networks, the liO, Aléop and Rémi regional coaches, Réunion, Martinique and
+  French Guiana. Each is the keyless vehicle feed of a transport.data.gouv.fr
+  record under Licence Ouverte 2.0 or ODbL, recorded in the registry and
+  DATA_SOURCES.md. Trams and boats take their own mode, feeds that publish
+  km/h (Dijon, Le Mans, Bourg-en-Bresse, Blois, Montluçon) are converted to
+  m/s, and internal route keys read as the line on the vehicle. Networks
+  already in the layer are not added a second time (#1716).