docs(all): getting started section, beta release warning

[saragerion]

Description of your changes

• Added readme files with minimal content for each package (including root)
• Added installation guide
• Added notice/warning about beta and unstable version
• Added third party licenses notice

How to verify this change

Readme files:
https://github.com/awslabs/aws-lambda-powertools-typescript/blob/ba37617b4d5ea2622e726c2c3541c904e52d13dc/README.md

MKDOCS: see local buid.

Related issues, RFCs

#349

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published in downstream module
• The PR title follows the conventional commit semantics

Breaking change checklist

N/A

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By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[dreamorosi]

Intro + disclaimers on the documentation look great :)

[saragerion]

I removed this one because I realized it was a python library