gen_makefile: add example to end of --help
diff --git a/gen_makefile.py b/gen_makefile.py
index 1a8b751..85e1ab7 100755
--- a/gen_makefile.py
+++ b/gen_makefile.py
@@ -38,6 +38,13 @@
 
 By default, it is assumed that your user has write permission to /usr/local. If you
 need sudo to install there, you may issue the --sudo-make-install option.
+
+EXAMPLE:
+
+  ./gen_makefile.py 3G+2G.deps default.opts iu.opts -I -m build
+  cd build
+  make
+
 '''
 
 import sys