docs: Reference build and install from README

[matschaffer-roblox]

Replaces the somewhat-incomplete build instructions from the main README with a link to the official documentation.

Related to #6003 (comment)

When I saw the docs in the readme, I tried to apply them directly, but they don't work on macos without some additional homebrew packages.

The official docs (especially https://docs.fluentbit.io/manual/installation/macos#install-build-dependencies) make this much clearer.

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[patrick-stephens]

Can you sort the DCO @matschaffer-roblox as it's required to merge I'm afraid?

[matschaffer-roblox]

@patrick-stephens looks like I should be set on DCO. Let me know if you need anything else.

[matschaffer-roblox]

Thanks @patrick-stephens ! I'm not entirely sure but seems like the commit message checker might have been flagging the PR subject so I updated it to match ^[a-z0-9A-Z\-_\s\,\.\/]+\:[ ]{0,1}[a-zA-Z]+[a-zA-Z0-9 \-\.\:_\#\(\)=\/'\"\,><\+\[\]\!\*\\]+$ - I think you probably have to re-run on your end.