List recipes as tree with `just --tree`.

Hi there!
Is there a way to quickly check the recipe dependencies?
I checked the [Listing Available Recipes](https://just.systems/man/en/chapter_24.html) page but it's not mentioned.

If not existing, I think it could be worth to implement.
Let's take an example.
Based on this `Justfile` found in the [documentation](https://just.systems/man/en/chapter_40.html) :
```sh
# Justfile
a:
echo 'A!'

b: a
echo 'B start!'
just c
echo 'B end!'

c:
echo 'C!'
```

We could execute the following command :
```sh
just --list --graph
```

And we could clearly see the recipe dependencies :
```sh
├── a
├── b
│ ├── a
│ └── c
└── c
```

What do you think?