Add play section.

README.md

@@ -14,3 +14,54 @@ OpenFlow switch liveness monitor.
 [codeclimate]: https://codeclimate.com/github/trema/switch_monitor
 [gemnasium]: https://gemnasium.com/trema/switch_monitor
 [inch]: http://inch-ci.org/github/trema/switch_monitor
+
+Install
+-------
+
+```
+$ git clone https://github.com/trema/switch_monitor.git
+$ cd switch_monitor
+$ bundle install
+```
+
+
+Play
+----
+
+Run this controller:
+
+```
+% bundle exec trema run ./lib/switch_monitor.rb -c trema.conf
+All switches =
+Switch 0x3 is UP
+Switch 0x2 is UP
+Switch 0x1 is UP
+All switches = 0x1, 0x2, 0x3
+...
+```
+
+On another terminal, stop and restart running switches with `trema
+kill` and `trema up` command, and switch_monitor.rb outputs the
+current switch status.
+
+```
+(On another terminal)
+% bundle exec trema kill 0x1
+% bundle exec trema up 0x1
+```
+
+```
+% bundle exec trema run ./lib/switch_monitor.rb -c trema.conf
+All switches =
+Switch 0x3 is UP
+Switch 0x2 is UP
+Switch 0x1 is UP
+All switches = 0x1, 0x2, 0x3
+...
+Switch 0x1 is DOWN
+All switches = 0x2, 0x3
+...
+Switch 0x1 is UP
+```
+
+Enjoy!