Document water_name and waterway

layers/water_name/README.md

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+# water_name
+
+Lake center lines for labelling lake bodies.
+This is based of the [osm-lakelines](https://github.com/lukasmartinelli/osm-lakelines) project
+which derives nice centerlines from OSM water bodies. Only the most important lakes contain labels.
+
+## Fields
+
+- **name_en**: The english `name:en` value if available.
+- **name**: The OSM [`name`](http://wiki.openstreetmap.org/wiki/Key:name) value of the water body.
+- **class**: At the moment only `lake` since no ocean parts are labelled. *Reserved for future use*.
+
+
+