Add doc for WKB POINT EMPTY handling

web/content/specifications/wkb.md

@@ -73,6 +73,13 @@ LinearRing {
 };
 ```
 
+### Empty Geometries
+
+For most geometry types, empty geometries are indicated naturally by having `numPoints` = 0.
+Points do not have a `numPoints` field, so `POINT EMPTY` is represented by a `Point` 
+with each ordinate value set to an IEEE-754 quiet NaN value
+(big endian 0x7ff8000000000000 or little endian 0x000000000000f87f).
+
 ### Geometry Types
 
 GEOS only supports the seven original simple features geometry types.