Removal of the `python-on-whales` command

The `python-on-whales` command is not available anymore, meaning that you cannot download the docker client binary automatically.
You need to install it yourself by using the Docker installation guide: https://docs.docker.com/engine/install/ . Note that you need only the client, you can skip the installation of the full docker engine. For example, on Ubuntu, that means you just need to do
```
sudo apt-get install docker-ce-cli docker-buildx-plugin docker-compose-plugin
```

instead of
```
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
```

The issue points to the Docker installation guide and shows Ubuntu commands for installing only the Docker client. Start by locating project documentation that describes installing or downloading the Docker CLI. Done means the documentation no longer refers to the unavailable python-on-whales command and clearly explains the client-only installation path.

Written by the indexing model from the issue text.