UPNP example produces error, method description needs clarification

**Your Godot version:** stable, latest

**Issue description:**
>
> const PORT = 7777
> var upnp = UPNP.new()
> upnp.discover(2000, 2, "InternetGatewayDevice")
> upnp.add_port_mapping(port)
>
> To close a specific port (e.g. after you have finished using it):
>
> upnp.delete_port_mapping(port)

I would think instead it should say (port -> PORT):

```
const PORT = 7777
var upnp = UPNP.new()
upnp.discover(2000, 2, "InternetGatewayDevice")
upnp.add_port_mapping(PORT)
```

and
```
upnp.delete_port_mapping(PORT)
```

The [discover method](https://docs.godotengine.org/en/latest/classes/class_upnp.html#class-upnp-method-discover) is probably the most important here, as without it, you won't be able to do anything with UPNP. Unfortunately I find the description of the methods arguments very lacking:

> timeout is the time to wait for responses in milliseconds. ttl is the time-to-live; only touch this if you know what you're doing.

Questions I have:
**timeout**:
Why is the default 2 seconds? What is the downside of using 1 second or even 0.5? Having shorter wait time makes a big difference in how the games responsiveness feels during login. 1 second seems to work fine for me and even 0.5. But I would like to know the risks, pros and cons of changing this value.
**ttl**:
"only touch this if you know what you're doing" - this description is not helpful at all in an API documentation and at best might seems condescending to who want to learn and improve their skills.

**URL to the documentation page:**
https://docs.godotengine.org/en/latest/classes/class_upnp.html#class-upnp-method-discover