Maintenance: README files, beta release warnings

[saragerion]

Description of the feature request

• Add readme files with minimal content for each package (including root)
• Add installation guide
• Add notice about beta

Problem statement

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Summary of the feature

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Code examples

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Benefits for you and the wider AWS community

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Describe alternatives you've considered

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Additional context

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Related issues, RFCs

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[github-actions]

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