[libs][arch] update e_side comment

Author: amin1377

libs/libarchfpga/src/switchblock_types.h

@@ -18,7 +18,8 @@ enum e_directionality {
 /**
  * @brief At the intersection of routing channels, left, right, top and bottom specify the x- and y-directed channels
  * while above and under specify the switch block wires one a layer above or below the current one. above and below
- * are only used for multi-layer FPGAs. 
+ * are only used for multi-layer FPGAs. Note that the order of 2D sides is important, as it corresponds to the bit 
+ * order in t_rr_node_data::dir_side_.sides.
  */
 enum e_side : unsigned char {
     TOP = 0,