Improve instructions for enabling visualizer on examples

src/visualizer/examples/readme.txt

@@ -1,3 +1,9 @@
 For activating the visualizer, with any example, just pass the option
---SimulatorImplementationType=ns3::VisualSimulatorImpl to it, assuming
-the script uses ns-3's command line parser (class CommandLine).
+--SimulatorImplementationType=ns3::VisualSimulatorImpl to it, assuming the
+script uses ns-3's command line parser (class CommandLine), and add 'visualizer'
+as a module dependency to that program.
+
+Alternatively, run the example with waf --run adding the --visualize option.
+For example:
+
+./waf --run wifi-simple-adhoc-grid --visualize