Add name_de to documentation

layers/mountain_peak/mountain_peak.yaml

@@ -6,7 +6,8 @@ layer:
   srs: +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over
   fields:
     name: The OSM [`name`](http://wiki.openstreetmap.org/wiki/Key:name) value of the peak.
-    name_en: The english `name:en` value if available.
+    name_en: English name `name:en` if available, otherwise `name`.
+    name_de: German name `name:de` if available, otherwise `name` or `name:en`.
     elev_m: Elevation (`ele`) in meters.
   datasource:
     geometry_field: geometry