Add details in `--dev` cli flag documentation (#2305)

add details in `--dev` flag to tell that it disables local peer
discovery

### Context

When adding automated end-to-end tests, we replaced `--dev` by 

```
`--chain=dev`, `--force-authoring`, `--rpc-cors=all`, `--alice`, and `--tmp` flags
```

as stated in the command line documentation. But the tests started
failing due to the nodes connecting to each other.

### Fix

This PR includes additional command line documentation to explain more
in detail what `--dev` flag inludes.