docs: correct README typos (fixes #2473)

[abuzarkhaaan]

What I did

1.Fixes spelling of ‘distributed’ and adds Oxford comma.

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Latest commit: 7640fdc

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[gerjanvangeest]

Why the double dot?

Suggested change

	- **Modern Code:** Lion is distributed as pure ES modules..
	- **Modern Code:** Lion is distributed as pure ES modules.