Updating readme with diagnostic-channel information

README.md

@@ -136,6 +136,14 @@ var otherClient = appInsights.getClient("<other_instrumentation_key>");
 otherClient.trackEvent("custom event");
 ```
 
+### Automatic third-party instrumentation
+
+In order to track context across asynchronous calls, some changes are required in third party libraries such as mongodb and redis. By default ApplicationInsights will use `diagnostic-channel-publishers` to monkey-patch some of these libraries. This can be disabled by setting the `APPLICATION_INSIGHTS_NO_DIAGNOSTIC_CHANNEL` environment variable. Note that by setting that environment variable, events may no longer be correctly associated with the right operation.
+
+Currently there are 6 packages which are instrumented: `bunyan`, `console`, `mongodb`, `mongodb-core`, `mysql` and `redis`.
+
+The `bunyan` package and `console` messages will generate Application Insights Trace events based on whether `setAutoCollectConsole` is enabled. The `mongodb`, `mysql` and `redis` packages will generate Application Insights Dependency events based on whether `setAutoCollectDependencies` is enabled.
+
 ## Examples
 
 ### Tracking dependency