Cite code lesson: Add how to add a citation.cff file to a GitHub repo

[lwasser]

In the cite code lesson, we do a nice job of overviewing how to connect a GitHub repo to Zenodo. However, adding a citation file needs to be fleshed out further. I believe there is a tool to help create the file that we can reference.

It would be nice to add

• steps for how to add the file
• ideally using a resource that helps someone create a properly formatted file. We can use this tool to create the file - We just need to walk people through how to do it.