[Docs] Missing env setup in remote example

### Description

In [Running your workflow](https://www.union.ai/docs/v1/flyte/user-guide/getting-started/running-your-workflow/), commands for remote running missed env input, which cause remote error like:

```
File "/root/hello_world.py", line 19, in
registry=os.environ['FLYTE_IMAGE_REGISTRY']
```

This would work at my local machine:

```
FLYTE_IMAGE_REGISTRY=localhost:30000 pyflyte run --env FLYTE_IMAGE_REGISTRY=localhost:30000 --remote --project my-project --domain development hello_world.py hello_world_wf
```

### Are you sure this issue hasn't been raised already?

- [x] Yes

### Have you read the Code of Conduct?

- [x] Yes