[Need support]: Point getting-started at customize.sh instead of manual steps

[TKaltofen]

What and why

docs/getting-started.md ("After Creating Your Repository") still walks readers through the manual customization steps (rename placeholder/, edit pyproject.toml, edit .releaserc.yaml, rewrite imports), while the README and CLAUDE.md recommend running bin/customize.sh, which does all of that in one shot. New users following getting-started do redundant, error-prone manual work.

Pointers

• docs/getting-started.md, steps 2 to 5 of "After Creating Your Repository"
• README.md, "Setup Your Plugin" step 1 (the canonical customize.sh instructions)

Steps

1. Replace the manual steps with a single step pointing at bin/customize.sh and the README section, keeping the verify (tox), file-removal, and repository-settings steps.
2. Skim the rest of the file for other statements that predate customize.sh.

Acceptance criteria

• getting-started no longer instructs manual renames that customize.sh performs.
• The remaining steps match the README's setup flow.

Notes

This project uses semantic versioning driven by Conventional Commits, so the PR title matters: use docs: point getting-started at customize.sh.

New to the project? This issue is a good entry point, we are happy to help in the comments.

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