Updated release notes in README.txt

Author: pdavidc

README.txt

@@ -70,6 +70,7 @@ New features and improvements in World Wind Java SDK 2.1.0
 - Repaired WWJ-537, Surface shape lines appear dashed when viewed obliquely.
 - Repaired an issue where AnalyticSurface returns an incorrect picked object when the altitude mode is CLAMP_TO_GROUND.
 - Added ability to retrieve elevations via WCS. Added WCSElevations example.
+- Added image texture support to SurfacePolygon.
 - Modified CompoundElevationModel to sort elevation models from lowest resolution to highest when models are added.
 - Modified SurfaceImage to optionally display on top of surface shapes, via the alwaysOnTop property.