Add explanations to wms-custom-proj example

examples/wms-custom-proj.js

@@ -10,6 +10,10 @@ goog.require('ol.source.TileWMS');
 
 
 
+// By default OpenLayers does not know about the EPSG:21781 (Swiss) projection.
+// So we create a projection instance for EPSG:21781 and pass it to
+// ol.proj.addProjection to make it available to the library.
+
 var projection = new ol.proj.Projection({
   code: 'EPSG:21781',
   // The extent is used to determine zoom level 0. Recommended values for a
@@ -18,6 +22,11 @@ var projection = new ol.proj.Projection({
   units: 'm'
 });
 ol.proj.addProjection(projection);
+
+// We also declare EPSG:21781/EPSG:4326 transform functions. These functions
+// are necessary for the ScaleLine control and when calling ol.proj.transform
+// for setting the view's initial center (see below).
+
 ol.proj.addCoordinateTransforms('EPSG:4326', projection,
     function(coordinate) {
       return [