PHOENIXD_URL

In the config file is this:

```
## URL of your `phoenixd` instance. Note the username (`satoshi` here)
## is not used, but you have to set it to something. `satoshi` or `_` work we>
## Your `phoenixd` instance will put its password in `~/.phoenix/phoenix.conf`
PHOENIXD_URL=http://_:hunter2@127.0.0.1:9740
```

Can you provide more info on how to get the PHOENIXD_URL ?