Fix docs: use crates/matchy for cargo install --path

[J-Gras]

Description

Fix documentation for installing the CLI from source. The repo root Cargo.toml is a workspace manifest (no [package]), so cargo install --path . fails with "found a virtual manifest ... instead of a package manifest". The docs now use cargo install --path crates/matchy, which installs the matchy binary from the main crate.

Updated:

• book/src/getting-started/installation.md – "From source" section
• book/src/getting-started/cli-installation.md – "Installing from source" section
• book/src/dev/building.md – "Quick Build" / Install CLI step

Fixes # (issue)

Type of Change

• 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 not work as expected)
• Documentation update
• Performance improvement
• Refactoring (no functional changes)

How Has This Been Tested?

• Existing test suite passes (cargo test)
• Added new tests for new functionality
• Tested on multiple platforms (Linux, macOS, Windows)
• Ran benchmarks to verify performance (cargo bench)
• Tested C FFI integration (if applicable)

(Docs-only change; verified install command works from repo root.)

Checklist

• My code follows the style guidelines of this project (cargo fmt)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings (cargo clippy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• I have updated CHANGELOG.md (if applicable)

Performance Impact

N/A – documentation only.

Breaking Changes

None.

Additional Context

.github/workflows/deploy-docs.yml correctly uses cargo install --path . from inside book/mdbook-project-version (a separate package); no change there.