Add htmx guidelines (#28993)

To make sure we don't abuse it.

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

docs/content/contributing/guidelines-frontend.en-us.md

@@ -65,14 +65,17 @@ Recommended implementations:
 
 * Vue + Vanilla JS
 * Fomantic-UI (jQuery)
+* htmx (partial page reloads for otherwise static components)
 * Vanilla JS
 
 Discouraged implementations:
 
 * Vue + Fomantic-UI (jQuery)
 * jQuery + Vanilla JS
+* htmx + any other framework which requires heavy JS code, or unnecessary features like htmx scripting (`hx-on`)
 
 To make UI consistent, Vue components can use Fomantic-UI CSS classes.
+We use htmx for simple interactions. You can see an example for simple interactions where htmx should be used in this [PR](https://github.com/go-gitea/gitea/pull/28908). Do not use htmx if you require more advanced reactivity, use another framework (Vue/Vanilla JS).
 Although mixing different frameworks is discouraged,
 it should also work if the mixing is necessary and the code is well-designed and maintainable.