Added htmx before transition reference link (#2929)

This is missing from the reference page but properly documented on the events page. This simply links the two together so anyone can quickly jump between the two.

Milestone: patch

www/content/reference.md

@@ -142,6 +142,7 @@ All other attributes available in htmx.
 | [`htmx:beforeRequest`](@/events.md#htmx:beforeRequest)  | triggered before an AJAX request is made
 | [`htmx:beforeSwap`](@/events.md#htmx:beforeSwap)  | triggered before a swap is done, allows you to configure the swap
 | [`htmx:beforeSend`](@/events.md#htmx:beforeSend)  | triggered just before an ajax request is sent
+| [`htmx:beforeTransition`](@/events.md#htmx:beforeTransition)  | triggered before the [View Transition](https://developer.mozilla.org/en-US/docs/Web/API/View_Transitions_API) wrapped swap occurs
 | [`htmx:configRequest`](@/events.md#htmx:configRequest)  | triggered before the request, allows you to customize parameters, headers
 | [`htmx:confirm`](@/events.md#htmx:confirm)  | triggered after a trigger occurs on an element, allows you to cancel (or delay) issuing the AJAX request
 | [`htmx:historyCacheError`](@/events.md#htmx:historyCacheError)  | triggered on an error during cache writing