Layout bugs in tutorial web page "POSTing to the backend" section

[japhb]

Near the top of the POSTing to the backend section of the tutorial web page, there are two layout bugs:

1. The two-element list of what to do is laid out as a single paragraph
2. The first code block has a spurious trailing ```

[Altai-man]

Fixed in croservices/cro@fae3b13, will be deployed when possible.