add etldoc to layer_waterway

gen_etl_graph_waterway.sh

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