docs: add setup guide for bun

[Marukome0743]

Description

Add a new ‘bun’ section to the local setup guide for installing Husky and configuring a commitlint hook

Documentation:

• Introduce a ‘bun’ guide showing how to install Husky and initialize its hooks
• Show how to add a commitlint hook with bunx, including a Windows-specific command variation

Motivation and Context

#4383 added CLI instruction for Bun package manager.
However, the setup guide didn't updated.

Usage examples

bun add --dev husky
bunx husky install
# Add commit message linting to commit-msg hook
echo "bunx commitlint --edit \$1" > .husky/commit-msg
# Windows users should use ` to escape dollar signs
echo "bunx commitlint --edit `$1" > .husky/commit-msg

How Has This Been Tested?

I have tested on my local PC.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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