Add `signoff-on-commit` option 📖📃⚙️

What's Changed

🧰 Maintenance

• Set signoff-on-commit if actor is owner by @norwd in #17
• Add signoff-on-commit input to toggle -s flag by @norwd in #18

📖 Documentation

• Document the signoff-on-commit option by @norwd in #19
• Correct the comment character in the YAML example by @norwd in #20

Other Changes

• Prevent empty list items in config by @norwd in #16

Full Changelog: v1.1.5...v1.1.6