fix: update digital ocean token configuration variable and insert warning

[qdzlug]

Proposed changes

This is a stop-gap measure to help with #208 - if the user has not specified the DIGITALOCEAN_TOKEN we will
warn them that it also needs to be in the environment.

Additional changes will make this a bit neater, but this will address it in the short term.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have written my commit messages in the Conventional Commits format.
• I have read the CONTRIBUTING doc
• I have added tests (when possible) that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[4141done]

This looks good. As always we have the caveat of the need for some more centralized specification for all of this config but as a bug fix this seems good. Some small suggestions and questions for my own learning but nothing blocking.