Missing/incomplete docs

[thislooksfun]

This isn't actually a bug, but there wasn't a "docs" issue template. Some of the documentation is incomplete or out of date.

Incomplete:

• https://github.com/joshwilsonvu/eslint-plugin-solid/blob/main/docs/prefer-classlist.md -- missing description for classnames key
• https://github.com/joshwilsonvu/eslint-plugin-solid/blob/main/docs/self-closing-comp.md -- bad code formatting in table
• Most keys would benefit from a 'default value' column, especially boolean keys, even if the default value seems obvious

Missing:

• https://github.com/joshwilsonvu/eslint-plugin-solid/blob/main/docs/prefer-show.md

[joshwilsonvu]

Thanks for the feedback! I've added descriptions and defaults to all options and updated the options format in the docs.