chore(serverless): Fix incorrect path in Readme (#6212)

This patch fixes an incorrect path for requiring the auto-init script in the `@sentry/serverless` Readme for users who want to set up the layer via the ARN and environment variables. Furthermore, this patch slightly enhances the step to find the correct ARN by linking to our (still kinda broken) ARN dropdown in the docs.

packages/serverless/README.md

@@ -59,7 +59,7 @@ Another and much simpler way to integrate Sentry to your AWS Lambda function is
 1. Choose Layers -> Add Layer.
 2. Specify an ARN: `arn:aws:lambda:us-west-1:TODO:layer:TODO:VERSION`.
 3. Go to Environment variables and add:
-   - `NODE_OPTIONS`: `-r @sentry/serverless/cjs/awslambda-auto`.
+   - `NODE_OPTIONS`: `-r @sentry/serverless/build/npm/cjs/awslambda-auto`.
    - `SENTRY_DSN`: `your dsn`.
    - `SENTRY_TRACES_SAMPLE_RATE`: a number between 0 and 1 representing the chance a transaction is sent to Sentry. For more information, see [docs](https://docs.sentry.io/platforms/node/guides/aws-lambda/configuration/options/#tracesSampleRate).