Adjusting docs for hx-ext

[zachczx]

Hi, I read the hx-ext docs while doing stuff, and I thought it can be made clearer with an example for those who have multiple extensions. If it's alright I can submit a pull request with my proposed edits, which are very minor. It'll just be an example with comma separated html attribute.

[Telroshan]

Documentation improvements are always welcome, so please feel free to open a PR! This doesn't mean we will necessarily merge it, but it'll be way easier to discuss & refine over a PR's code diff