Add generated README for highway name docs

layers/highway_name/README.md

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+# highway_name
+
+This is the layer for labelling the highways. Only highways that are named `name=*` and are long enough
+to place text upon appear. The OSM roads are stitched together if they contain the same name
+to have better label placement than having many small linestrings.
+For motorways you should use the `ref` field to label them while for other roads you should use `name`.
+
+## Fields
+
+- **ref**: The OSM [`ref`](http://wiki.openstreetmap.org/wiki/Key:ref) tag of the motorway or road.
+- **ref_length**: Length of the `ref` field. Useful for having a shield icon as background for labeling motorways.
+- **name**: The OSM [`name`](http://wiki.openstreetmap.org/wiki/Highways#Names_and_references) value of the highway.
+- **subclass**: Original value of the [`highway`](http://wiki.openstreetmap.org/wiki/Key:highway) tag. Use this to do more
+precise styling.
+- **class**: Either `motorway`, `major_road` (containing `trunk`, `primary`, `secondary` and `tertiary` roads) and `minor_road` (less important roads in the hierarchy like `residential` or `service`) or `path` for
+non vehicle paths (such as `cycleway` or `footpath`).
+
+
+