Missing code block in `declare-an-experiment-to-observe-the-weakness`

[Ciaran Sweet]

The section here https://chaostoolkit.org/reference/tutorial/#declare-an-experiment-to-observe-the-weakness is missing the json that is meant to be populating it:

chaostoolkit-documentation/sources/reference/tutorial.md

Lines 111 to 114 in e18cb5c

 ```json 
 {!code/tutorials/a-simple-walkthrough/experiment.json!} 
  
 ``` 

[Ciaran Sweet]

We're missing out the git submodule update --init call that should be here

chaostoolkit-documentation/.github/workflows/build.yaml

Lines 60 to 61 in e18cb5c

         git clone https://$GH_USER_NAME:$[e-mail]/chaostoolkit/chaostoolkit-documentation.git . 
         git checkout gh-pages