Adjust image size. Add explanatory text.

build.sh

@@ -56,7 +56,10 @@ run-dot() {
   which dot >/dev/null || die "$msg"
 
   log "Running dot"
-  dot -Tpng -o $out $in
+  # width, height
+  dot \
+    -Tpng -Gsize='2,4!' -Gdpi=300 \
+    -o $out $in
 }
 
 # Scan for TODOs.  Does this belong somewhere else?

doc/tutorial.md

@@ -19,6 +19,11 @@ It takes a minute or so to run.  The dependencies listed in the
 
 It should look like [this][example].
 
+This diagram shows what processes and files are involved in the demo.  Ovals
+represent processes; rectangles represent data.  The dotted lines denote
+components that are involved in the simulation, but wouldn't be used in a
+"real" setting.
+
 <img src="tools.png" alt="Diagram of RAPPOR Tools" />
 
 We simulate both the client and the server.  For the client, we: