Website: git pre-commit hook should use `xargs -r`

[ttencate]

git diff --name-only --cached --relative | grep '\.jsx\?$' | xargs -r standard
                                                                   ^^

This way, xargs won't run standard if no JavaScript files were changed in this commit. This is useful because without arguments, standard needlessly checks everything.

[Flet]

Nice! Would you mind updating the README in this repo? The website gets its content from here. I'll happily merge it!