Include some concrete usage examples in the README

Author: wangzhen127

README.md

@@ -118,6 +118,26 @@ node-problem-detector --apiserver-override=http://APISERVER_IP:APISERVER_INSECUR
 
 For more scenarios, see [here](https://github.com/kubernetes/heapster/blob/master/docs/source-configuration.md#kubernetes)
 
+## Try It Out
+You can try node-problem-detector in a running cluster by injecting messages to the logs that node-problem-detector is watching. For example, Let's assume node-problem-detector is using [KernelMonitor](https://github.com/kubernetes/node-problem-detector/blob/master/config/kernel-monitor.json). On your workstation, run ```kubectl get events -w```. On the node, run ```sudo sh -c "echo 'kernel: BUG: unable to handle kernel NULL pointer dereference at TESTING' >> /dev/kmsg"```. Then you should see the ```KernelOops``` event.
+
+When adding new rules or developing node-problem-detector, it is probably easier to test it on the local workstation in the standalone mode. For the API server, an easy way is to use ```kubectl proxy``` to make a running cluster's API server available locally. You will get some errors because your local workstation is not recognized by the API server. But you should still be able to test your new rules regardless.
+
+For example, to test [KernelMonitor](https://github.com/kubernetes/node-problem-detector/blob/master/config/kernel-monitor.json) rules:
+1. ```make``` (build node-problem-detector locally)
+2. ```kubectl proxy --port=8080``` (make a running cluster's API server available locally)
+3. Update [KernelMonitor](https://github.com/kubernetes/node-problem-detector/blob/master/config/kernel-monitor.json)'s ```logPath``` to your local kernel log directory. For example, on some Linux systems, it is ```/run/log/journal``` instead of ```/var/log/journal```.
+3. ```./bin/node-problem-detector --logtostderr --apiserver-override=http://127.0.0.1:8080?inClusterConfig=false --system-log-monitors=config/kernel-monitor.json  --port=20256``` (or point to any API server address:port)
+4. ```sudo sh -c "echo 'kernel: BUG: unable to handle kernel NULL pointer dereference at TESTING' >> /dev/kmsg"```
+5. You can see ```KernelOops``` event in the node-problem-detector log.
+6. ```sudo sh -c "echo 'kernel: INFO: task docker:20744 blocked for more than 120 seconds.' >> /dev/kmsg"```
+7. You can see ```DockerHung``` event and condition in the node-problem-detector log.
+8. You can see ```DockerHung``` condition at [http://127.0.0.1:20256/conditions](http://127.0.0.1:20256/conditions).
+
+**Note**:
+- You can see more rule examples under [test/kernel_log_generator/problems](https://github.com/kubernetes/node-problem-detector/tree/master/test/kernel_log_generator/problems).
+- For [KernelMonitor](https://github.com/kubernetes/node-problem-detector/blob/master/config/kernel-monitor.json) message injection, all messages should have ```kernel: ``` prefix (also note there is a space after ```:```).
+
 # Links
 * [Design Doc](https://docs.google.com/document/d/1cs1kqLziG-Ww145yN6vvlKguPbQQ0psrSBnEqpy0pzE/edit?usp=sharing)
 * [Slides](https://docs.google.com/presentation/d/1bkJibjwWXy8YnB5fna6p-Ltiy-N5p01zUsA22wCNkXA/edit?usp=sharing)