Make url Quickstart guide more user friendly

We need to update quickstart tutorial to make an app available on http://localhost:40000/ instead of http://localhost:40000/tasks, because some users may try to open the root of the server when they see such log message:

```
[19:41:00] weblocks/server server.lisp (start-server) -
Starting webserver on WEBLOCKS/SERVER::INTERFACE: "localhost"
WEBLOCKS/SERVER::PORT: 40000 DEBUG: T
#
```

and right now they will see an empty page saying:

```
File "/" was not found.
```

**Alternatively, we may** fix not the documentation but Weblocks, by making it to handle `/` route as special and showing a list of all of the available apps if none of them is bound to the `/` route. This will also help users who are making their apps themselves, not by following a quickstart guide.