add etldoc to layer_landcover

gen_etl_graph_landcover.sh

@@ -0,0 +1,19 @@
+
+
+DOT=landcover.dot
+
+echo "digraph G
+{    
+rankdir=LR;
+" > $DOT
+
+cat ./layers/landcover/mapping.yaml   | grep    "# etldoc:" |  sed 's/# etldoc://g'  >>$DOT
+cat ./layers/landcover/landcover.sql  | grep "\-\- etldoc:" |  sed 's/-- etldoc://g' >>$DOT
+
+echo "
+}
+" >> $DOT
+
+cat $DOT
+
+dot -Tpng $DOT > layer_landcover_etl.png