Add section about lefthook/pre-commit/prek with pixi

[pavelzw]

lefthook example config:

templates:
  run: run --as-is --quiet --no-progress
no_auto_install: true
pre-commit:
  fail_on_changes: always
  jobs:
    - name: pixi-install
      run: pixi install
    - group:
        parallel: true
        jobs:
          - name: ruff-check
            glob: "*.{py,pyi}"
            run: pixi {run} ruff check --fix --exit-non-zero-on-fix --force-exclude
          # ...