Make it easier to discover that data languages (JSON, YAML) and prose (Markdown) are not reported by default

[spenserblack]

Summary 💡

I'm not sure what the best way to do this is, but I'm thinking it can be included in the long help message output by onefetch --help to at least be a little easier to discover. Perhaps we can include examples of what "data" and "prose" includes.

Or perhaps we can document some FAQs somewhere.

Motivation 🔦

We've had many users, most recently @fenio in #26 (comment), get confused when their project's primary language isn't reported.

[o2sh]

By the way, it might be a good idea to update onefetch.dev and include the language type for each entry 🤔

[o2sh]

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