Add comments for pred_mv_sad and color_sensitivity

Change-Id: Id7b942c3b967208a7096c1042066c5333cfa7b6e

av1/encoder/block.h

diff --git a/av1/encoder/block.h b/av1/encoder/block.h
index befbce0..aaf3654 100644
--- a/av1/encoder/block.h
+++ b/av1/encoder/block.h
@@ -1044,8 +1044,9 @@
   int pred_mv_sad[REF_FRAMES];
   //! The minimum of \ref pred_mv_sad.
   int best_pred_mv_sad;
-  //! The sad of the 2 mv refs.
+  //! The sad of the 1st mv ref (nearest).
   int pred_mv0_sad[REF_FRAMES];
+  //! The sad of the 2nd mv ref (near).
   int pred_mv1_sad[REF_FRAMES];
 
   /*! \brief Disables certain ref frame pruning based on tpl.
@@ -1238,6 +1239,7 @@
    * of moving color objects.
    */
   uint8_t color_sensitivity_sb[2];
+  //! Color sensitivity flag for the coding block.
   uint8_t color_sensitivity[2];
   /**@}*/