Merge pull request #140 from tilezen/buffered-terrain-docs

Add docs about tile size variants

Author: nvkelso

docs/use-service.md

@@ -34,12 +34,22 @@ http://tile.mapzen.com/mapzen/terrain/v1/normal/11/330/790.png?api_key=your-mapz
 https://tile.mapzen.com/mapzen/terrain/v1/terrarium/{z}/{x}/{y}.png?api_key=your-mapzen-api-key
 ```
 
+Supported optional tile size variants:
+
+  `https://tile.mapzen.com/mapzen/terrain/v1/{256,512,260,516}/terrarium/{z}/{x}/{y}.png`
+
+The 260 and 516 variants contain 2 pixels of buffering on each edge.
+
 ##### Normal
 
 ```
 https://tile.mapzen.com/mapzen/terrain/v1/normal/{z}/{x}/{y}.png?api_key=your-mapzen-api-key
 ```
 
+Supported optional tile size variants:
+
+  `https://tile.mapzen.com/mapzen/terrain/v1/{256,512}/normal/{z}/{x}/{y}.png`
+
 ##### GeoTIFF
 
 ```