[Update] Add comment

quadtree.c

@@ -132,9 +132,9 @@ node *quadtree_position(int32_t li, int32_t col, node *tree, int32_t depth)
     node *crt = tree;
     do
     {
-        int32_t ligne = (li >> depth) & 1;
-        int32_t colonne = (col >> depth) & 1;
-        int32_t index = (ligne << 1) | colonne;
+        int32_t line = (li >> depth) & 1; // shift bit for select only the bit of stage & 1 check first bit
+        int32_t column = (col >> depth) & 1; // shift bit for select only the bit of stage & 1 check first bit
+        int32_t index = (line << 1) | column;
 
         crt = crt->child[index];
         depth--;