docs(queues): warn that defaultJobOptions don't always work

It's very unobvious that `defaultJobOptions` apply to jobs being scheduled only sometimes.

If you schedule jobs via a `FlowProducer`, these defaults don't have any effect.

I'd love to fix that, but before we tackle that, I think it's best and easiest to point out the current behaviour in the docs.

See taskforcesh/bullmq#1034 for more in-depth explanation of this problem.

content/techniques/queues.md

@@ -500,7 +500,7 @@ The `forRoot()` method is used to register a `bull` package configuration object
 - `limiter: RateLimiter` - Options to control the rate at which the queue's jobs are processed. See [RateLimiter](https://github.com/OptimalBits/bull/blob/master/REFERENCE.md#queue) for more information. Optional.
 - `redis: RedisOpts` - Options to configure the Redis connection. See [RedisOpts](https://github.com/OptimalBits/bull/blob/master/REFERENCE.md#queue) for more information. Optional.
 - `prefix: string` - Prefix for all queue keys. Optional.
-- `defaultJobOptions: JobOpts` - Options to control the default settings for new jobs. See [JobOpts](https://github.com/OptimalBits/bull/blob/master/REFERENCE.md#queueadd) for more information. Optional.
+- `defaultJobOptions: JobOpts` - Options to control the default settings for new jobs. See [JobOpts](https://github.com/OptimalBits/bull/blob/master/REFERENCE.md#queueadd) for more information. Optional. **Note: These do not take effect if you schedule jobs via a FlowProducer. See [bullmq#1034](https://github.com/taskforcesh/bullmq/issues/1034) for explanation.**
 - `settings: AdvancedSettings` - Advanced Queue configuration settings. These should usually not be changed. See [AdvancedSettings](https://github.com/OptimalBits/bull/blob/master/REFERENCE.md#queue) for more information. Optional.
 
 All the options are optional, providing detailed control over queue behavior. These are passed directly to the Bull `Queue` constructor. Read more about these options [here](https://github.com/OptimalBits/bull/blob/master/REFERENCE.md#queue).