Modify README as part of build process rather than using SETUPTOOLS_SCM_PRETEND_VERSION

[paddyroddy]

Is Your Feature Request Related to a Problem? Please Describe

On Slack, from @ntessore:

Interesting, but I feel like we are just moving the "hack" to a different place. I was thinking along the lines of https://github.com/hynek/hatch-fancy-pypi-readme where the README modification is part of the build process itself. But that should really wait until we are at the "encore" stage of the project.

Describe the Solution You'd Like

No response

Describe Alternatives You've Considered

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Additional Context

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[paddyroddy]

Actually, I don't think this would work @ntessore. We won't have access to git tag --describe in there.