updated the custom plugin doc to clarify the usage for reason and message

Author: xmcqueen

docs/custom_plugin_monitor.md

@@ -10,3 +10,53 @@
 * `concurrency`: The plugin worker number, i.e., how many custom plugins will be invoked concurrently.
 * `enable_message_change_based_condition_update`: Flag controls whether message change should result in a condition update.
 * `skip_initial_status`: Flag controls whether condition will be emitted during plugin initialization.
+
+### Annotated Plugin Configuration Example
+
+```
+{
+  "plugin": "custom",
+  "pluginConfig": {
+    "invoke_interval": "30s",
+    "timeout": "5s",
+    "max_output_length": 80,
+    "concurrency": 3,
+    "enable_message_change_based_condition_update": false
+  },
+  "source": "ntp-custom-plugin-monitor",
+  "metricsReporting": true,
+  "conditions": [
+    {
+      "type": "NTPProblem",
+      "reason": "NTPIsUp",              // This is the default reason shown when healthy
+      "message": "ntp service is up"    // This is the default message shown when healthy
+    }
+  ],
+  "rules": [
+    {
+      "type": "temporary",              // These are not shown unless there's an
+                                        // event so they always relate to a problem.
+                                        // There are no defaults since there is nothing
+                                        // to show unless there's a problem.
+      "reason": "NTPIsDown",            // This is the reason shown for this event
+                                        // and the message shown comes from stdout.
+      "path": "./config/plugin/check_ntp.sh",
+      "timeout": "3s"
+    },
+    {
+      "type": "permanent",              // These are permanent and are shown in the Conditions section
+                                        // when running `kubectl describe node ...`
+                                        // They have default values shown above in the conditions section
+                                        // and also a reason for each specific trigger listed in this rules section.
+                                        // Message will come from default for healthy times
+                                        // and during unhealthy time message comes from stdout of the check.
+ 
+      "condition": "NTPProblem",        // This is the key to connect to the corresponding condition listed above
+      "reason": "NTPIsDown",            // and the reason shown for failures detected in this rule
+                                        // and message will be from stdout of the check.
+      "path": "./config/plugin/check_ntp.sh",
+      "timeout": "3s"
+    }
+  ]
+}
+```