Issue with following Getting Started instructions

### Describe the bug

I followed the "Getting Started" instructions to install CSET and found that the following command produced an issue:

```bash
cset bake -i air_temp.nc -o output/ -r air_temperature_spatial_plot.yaml
```

This was on this page: https://metoffice.github.io/CSET/getting-started/run-recipe.html

I think Conda installed an old version of CSET by default (see section below). I can fix this by installing from source, but thought it would be tricky if other less technical team members tried to use these docs.

### How to reproduce

Steps to reproduce the behaviour:

1. Follow the instructions at https://metoffice.github.io/CSET/getting-started/installation.html
2. Ran `conda create --name=cset --channel=conda-forge cset` and `conda activate cset`
3. Ran `cset --version` to verify install. Got `CSET v0.3.0`
4. Downloaded the YAML and .nc file at https://metoffice.github.io/CSET/getting-started/run-recipe.html
5. Ran `cset bake -i air_temp.nc -o output/ -r air_temperature_spatial_plot.yaml`
6. It returned the following:

```bash
$ cset bake -i air_temp.nc -o output/ -r air_temperature_spatial_plot.yaml
usage: cset [-h] [-v] [--version] {bake,graph,cookbook} ...
cset: error: unrecognized arguments: -i -o -r
```

### Expected behaviour

Expected the command to work