added dotfile

slides/graphviz/quad_img_simple.dot

+digraph G {
+    0 [label=" "]
+    sg1 [label="SG"]
+    sd1 [label="SD"]
+    ig1 [label="IG"]
+    id1 [label="ID"]
+    sg2 [label="21"]
+    sd2 [label="12"]
+    ig2 [label="9"]
+    id2 [label="7"]
+    sg3 [label="4"]
+    sd3 [label="4"]
+    ig3 [label="4"]
+    id3 [label="4"]
+    sg4 [label="1"]
+    sd4 [label="1"]
+    ig4 [label="1"]
+    id4 [label="1"]
+    sg5 [label="0"]
+    sd5 [label="31"]
+    ig5 [label="3"]
+    id5 [label="27"]
+  0->{sg1, sd1, ig1, id1}  [quadtree = "normal"]
+  sg1->{sg2, sd2, ig2, id2}  [quadtree = "normal"]
+  sd1->{sg3, sd3, ig3, id3}  [quadtree = "normal"]
+  ig1->{sg4, sd4, ig4, id4}  [quadtree = "normal"]
+  id1->{sg5, sd5, ig5, id5}  [quadtree = "normal"]
+}