Add remark-directive-rehype to list of plugins

[IGassmann]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

This adds remark-directive-rehype to the list of remark plugins. It enables Markdown directives to be parsed as HTML when using remark-directive and remark-rehype.

[wooorm]

Thanks! :)