add layer_building etldoc comments

gen_etl_graph_building.sh

@@ -0,0 +1,21 @@
+
+
+
+
+DOT=building.dot
+
+echo "digraph G
+{    
+rankdir=LR;
+" > $DOT
+
+cat ./layers/building/mapping.yaml    | grep    "# etldoc:" |  sed 's/# etldoc://g'  >>$DOT
+cat ./layers/building/building.sql    | grep "\-\- etldoc:" |  sed 's/-- etldoc://g' >>$DOT
+
+echo "
+}
+" >> $DOT
+
+cat $DOT
+
+dot -Tpng $DOT > layer_building_etl.png