feat(docs): Add some docs on worker

docs/content/docs/developer-guide/vendure-worker.md

@@ -0,0 +1,29 @@
+---
+title: "Vendure Worker"
+weight: 0
+showtoc: true
+---
+
+# Vendure Worker
+
+The Vendure Worker is a process which is responsible for running computationally intensive or otherwise long-running tasks in the background. For example updating a search index or performing image transformations.
+
+The worker is started by calling the `bootstrapWorker()` function with the same configuration as is passed to the main server `bootstrap()`:
+
+```TypeScript
+import { bootstrapWorker } from '@vendure/core';
+
+import { config } from './vendure-config';
+
+bootstrapWorker(config).catch(err => {
+    console.log(err);
+});
+```
+
+## Underlying architecture
+
+Internally, the Worker is an instance of a [NestJS microservice](https://docs.nestjs.com/microservices/basics). By default the TCP protocol is used to send messages to and receive reponses from the Worker, but other transports may be used such as Redis or gRPC.
+
+## Running on the main process
+
+There is an option `runInMainProcess` which, if set to `true` will cause the Worker to be bootstrapped along with the main application, without the need for a separate process running `bootstrapWorker`. This is mainly used for testing and development, and is not advised for production use, since it negates the benefits of running long tasks off of the main process.