Add link to the venue JSON from the venue list JSON

[nuest]

The venue overview JSON currently looks like this:

[
  {
    "Venue type": "journal",
    "Venue name": "GigaScience",
    "No. of codechecks": 2
  },
  {
    "Venue type": "community",
    "Venue name": "CODECHECK",
    "No. of codechecks": 8
  },
...

Each item should contain a link to the JSON of the checks:

[
  {
    "Venue type": "journal",
    "Venue name": "GigaScience",
    "No. of codechecks": 2
    "codechecks": "https://codecheck.org.uk/register/venues/journal/gigascience/register.json"
  },
...