Document name_* deprecation strategy (#1605)

This PR is a **documentation change only**. It documents the fact that `name:xx` values are present in the tiles and documents that `name_de` and `name_en` will be removed in a future release in favor of `name:de` and `name:en` respectively.

layers/mountain_peak/mountain_peak.yaml

@@ -8,8 +8,8 @@ layer:
   buffer_size: 64
   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: English name `name:en` if available, otherwise `name`.
+    name: The OSM [`name`](http://wiki.openstreetmap.org/wiki/Key:name) value of the peak. Language-specific values are in `name:xx`.
+    name_en: English name `name:en` if available, otherwise `name`. This is deprecated and will be removed in a future release in favor of `name:en`.
     name_de: German name `name:de` if available, otherwise `name` or `name:en`.
     class:
       description: |