docs: More node docs (#11076)

Some more node docs for v8, including:

* How to add custom OTEL instrumentation
* How to use with custom OTEL setup
* How to setup non-framework node apps

Author: mydea

docs/v8-node.md

@@ -78,6 +78,78 @@ See [New Performance APIs](./v8-new-performance-apis.md) for details.
 For now, ESM support is only experimental. For the time being we only fully support CJS-based Node application - we are
 working on this during the v8 alpha/beta cycle.
 
+### Using Custom OpenTelemetry Instrumentation
+
+While we include some vetted OpenTelemetry instrumentation out of the box, you can also add your own instrumentation on
+top of that. You can do that by installing an instrumentation package (as well as `@opentelemetry/instrumentation`) and
+setting it up like this:
+
+```js
+const Sentry = require('@sentry/node');
+const { GenericPoolInstrumentation } = require('@opentelemetry/instrumentation-generic-pool');
+const { registerInstrumentations } = require('@opentelemetry/instrumentation');
+
+Sentry.init({
+  dsn: '__DSN__',
+});
+
+// Afterwards, you can add additional instrumentation:
+registerInsturmentations({
+  instrumentations: [new GenericPoolInstrumentation()],
+});
+```
+
+### Using a Custom OpenTelemetry Setup
+
+If you already have OpenTelemetry set up yourself, you can also use your existing setup.
+
+In this case, you need to set `skipOpenTelemetrySetup: true` in your `init({})` config, and ensure you setup all the
+components that Sentry needs yourself. In this case, you need to install `@sentry/opentelemetry`, and add the following:
+
+```js
+const Sentry = require('@sentry/node');
+const { SentrySpanProcessor, SentryPropagator, SentryContextManager, SentrySampler } = require('@sentry/opentelemetry');
+
+// We need a custom span processor
+provider.addSpanProcessor(new SentrySpanProcessor());
+// We need a custom propagator and context manager
+provier.register({
+  propagator: new SentryPropagator(),
+  contextManager: new SentryContextManager(),
+});
+
+// And optionally, if you want to use the `tracesSamplingRate` or related options from Sentry,
+// you also need to use a custom sampler when you set up your provider
+const provider = new BasicTracerProvider({
+  sampler: new SentrySampler(Sentry.getClient()),
+});
+```
+
+## Plain Node / Unsupported Frameworks
+
+When using `@sentry/node` in an app without any supported framework, you will still get some auto instrumentation out of
+the box!
+
+Any framework that works on top of `http`, which means any framework that handles incoming HTTP requests, will
+automatically be instrumented - so you'll get request isolation & basic transactions without any further action.
+
+For any non-HTTP scenarios (e.g. websockets or a scheduled job), you'll have to manually ensure request isolation by
+wrapping the function with `Sentry.withIsolationScope()`:
+
+```js
+const Sentry = require('@sentry/node');
+
+function myScheduledJob() {
+  return Sentry.withIsolationScope(async () => {
+    await doSomething();
+    await doSomethingElse();
+    return { status: 'DONE' };
+  });
+}
+```
+
+This way, anything happening inside of this function will be isolated, even if they run concurrently.
+
 ## Express
 
 The following shows how you can setup Express instrumentation in v8. This will capture performance data & errors for