Update README

Goals

• Keep every README in the repo accurate for the current codebase.
• Ensure README explains the current chezmoi setup workflow.
• Ensure README includes the mise install step that runs after chezmoi apply.
• Ensure README explains the practical split between Homebrew and mise.
• Remove outdated or no-longer-true statements.
• Write in concise Japanese unless the user explicitly asks for another language.

Workflow

1. Discover README targets

• List README files with rg --files -g 'README*' from the repo root.
• Only the top-level README.md is permitted; subdirectory READMEs are not allowed.
• If any subdirectory README files exist, remove them and consolidate their content into the top-level README.

2. Determine scope for the README

• The top-level README.md must be the only README in the repo.
• Use the filesystem to confirm what exists before writing.

3. Rewrite the README

• Keep content minimal; include ## セットアップ.
• ## セットアップ
  • Describe the exact setup steps required now.
  • Install Homebrew by following the official installation instructions, then install chezmoi with brew install chezmoi.
  • Include copy-pasteable commands in Markdown code blocks so the setup can be executed directly.
  • After chezmoi --source ./chezmoi apply, include mise install -C ~.
  • Remove deprecated steps or tooling references.
  • Explain that Homebrew manages OS-level packages and mise manages versioned development tools.

4. Remove obsolete content

• Delete any badges, deprecated sections, or instructions that are no longer true.
• If a section cannot be substantiated from current files, remove it.

Output expectations

• Do not add extra sections unless the user explicitly asks for them.
• For the root README, never mention deprecated folders (like init/ or old Nix/Home Manager paths) or non-active folders unless instructed.
• Only README.md at repo root may exist; delete any others.

Notes

• This repo treats chezmoi/ as the active configuration root.
• The setup starts by installing Homebrew with the official installer, then installing chezmoi with Homebrew.
• The canonical dry-run/check command is chezmoi --source ./chezmoi diff.
• The canonical apply command is chezmoi --source ./chezmoi apply.
• The canonical mise tool installation command is mise install -C ~.
• If a README claims to manage files or scripts that no longer exist, remove those claims.