docs: Add guide on how to simulate real apps in ndnSIM

Change-Id: I3694a8791b9540fc1b926a83ff55421b47e0f2a2
diff --git a/docs/Doxyfile b/docs/Doxyfile
index dfe0463..b8d1823 100644
--- a/docs/Doxyfile
+++ b/docs/Doxyfile
@@ -764,7 +764,7 @@
                          doxygen.hpp
 
 # For example:
-# ../../../build/utils/ns3-dev-print-introspected-doxygen-debug --log --group Ndn > introspected-doxygen.hpp
+# ../../../build/utils/ns3-dev-print-introspected-doxygen-debug --group=Ndn > introspected-doxygen.hpp
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses