update dox

include/core/SkImageInfo.h

Index: include/core/SkImageInfo.h
diff --git a/include/core/SkImageInfo.h b/include/core/SkImageInfo.h
index b955433329579d6907da98a085e8b72759818fdf..17e1228e46232283aac0d0b1640b5037e38b249c 100644
--- a/include/core/SkImageInfo.h
+++ b/include/core/SkImageInfo.h
@@ -67,6 +67,10 @@ static inline bool SkAlphaTypeIsValid(unsigned value) {
 
 /**
  *  Describes how to interpret the components of a pixel.
+ *
+ *  kN32_SkColorType is an alias for whichever 32bit ARGB format is the "native"
+ *  form for skia's blitters. Use this if you don't have a swizzle preference
+ *  for 32bit pixels.
  */
 enum SkColorType {
     kUnknown_SkColorType,