Update nodejs.md

added a new section for sdk log collection/self diagnostics

Please refer to lines 455 to 472

I am an Engineer from the Application Insights team who built this lab and also contributed to TSGs 

I appreciate if the changes can be reviewed and published and, if my name is listed as a contributor to help me in my connect discussion.

Author: Ashi-Sunnam

articles/azure-monitor/app/nodejs.md

@@ -452,6 +452,27 @@ These properties are client specific, so you can configure `appInsights.defaultC
 | correlationIdRetryIntervalMs    | The time to wait before retrying to retrieve the ID for cross-component correlation. (Default is `30000`.)     |
 | correlationHeaderExcludedDomains| A list of domains to exclude from cross-component correlation header injection. (Default. See [Config.ts](https://github.com/Microsoft/ApplicationInsights-node.js/blob/develop/Library/Config.ts).)|
 
+##**How do I customize logs collection?**
+
+By default, Application Insights Node.js SDK logs at warning level to console.
+
+To spot and diagnose issues with Application Insights, "Self-diagnostics" can be enabled. This means collection of internal logging from Application Insights Node.js SDK.
+
+The following code demonstrates how to enable debug logging as well and generate telemetry for internal logs.
+
+let appInsights = require("applicationinsights");
+appInsights.setup("<YOUR_CONNECTION_STRING>")
+    .setInternalLogging(true, true) // Enable both debug and warning logging
+    .setAutoCollectConsole(true, true) // Generate Trace telemetry for winston/bunyan and console logs
+    .start();
+    
+Logs could be put into local file using APPLICATIONINSIGHTS_LOG_DESTINATION environment variable, supported values are file and file+console, a file named applicationinsights.log will be generated on tmp folder by default, including all logs, /tmp for *nix and USERDIR\\AppData\\Local\\Temp for Windows. Log directory could be configured using APPLICATIONINSIGHTS_LOGDIR environment variable.
+
+process.env.APPLICATIONINSIGHTS_LOG_DESTINATION = "file+console";
+process.env.APPLICATIONINSIGHTS_LOGDIR = "C:\\applicationinsights\\logs";
+
+// Application Insights SDK setup....
+
 ## Troubleshooting
 
 [!INCLUDE [azure-monitor-app-insights-test-connectivity](../../../includes/azure-monitor-app-insights-test-connectivity.md)]