Update contributing docs with guidelines for LLM code and unwanted features

Affected Page(s)

I think our Contributing docs could use some more specific boundaries.

What Could Be Better?

• Document practices around issues and code generated by LLMs.
  • Do we want these at all?
  • At the very least, I'd like some guardrails against contributors submitting LLM responses that they themselves don't understand.
• Document more boundaries around what kinds of features we won't accept.
  • For example, I don't want jrnl accessing anything over the internet, because I want to minimize the risk of data exfiltration, I do not want to support constantly-shifting online APIs, and it isn't concordant with the UNIX philosophy we're trying to follow.

Other Information

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