docs: update defaults example to valid lua

[xero]

I copy pasted the defaults from the README into my config when testing out the plugin and was greeted by an error. Wanted to help other lazy users like myself in the future.

When I took a look at the actual defaults files i noticed the sort_keys table was also missing from the README. I considered adding it to this pr, but assumed it was left out on purpose since there were no comments on these lines.