[typo] Replace 'mostly likely' with 'most likely'

[AntonioClarke]

Summary

I believe this is a typo, and that this text should say "most likely", as in LLMs try to write text that has the highest probability of coming next, as opposed to "mostly likely".

The only reference I can find to the difference between the two terms is here, that said, it appears to be more of a theoretical consideration, and a brief skim of the internet returns very few results for "mostly likely". It's unclear what it would mean in this context for the generated text to be "mostly likely" - if it did in fact mean "mostly likely" rather than "most likely", there are likely clearer ways of articulating that given the rarity of this phrase.

I did not list myself as an author in registry.yaml as updating a typo should likely not count as authorship. Please let me know if this should be changed.

Motivation

Not having typos is always better than having typos. This is obviously a marginal improvement, but given that the README for this repo explicitly said:

Whether you're submitting an idea, fixing a typo, adding a new guide, or improving an existing one, your contributions are greatly appreciated!

I assumed that this change would be worth putting up, and meets the "Relevance" bar

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[ted-at-openai]

Thanks Antonio! :)