fix: Correct user-event v13/v14 cross-links. (#985)

Author: make-github-pseudonymous-again

docs/ecosystem-user-event.mdx

@@ -12,7 +12,7 @@ advanced simulation of browser interactions than the built-in
 
 > This page describes `user-event@13.5.0`.
 If you are starting or actively working on a project,
-we recommend to use [`user-event@14.0.0-beta`](user-event/intro) instead, as it includes important bug fixes and new features.  
+we recommend to use [`user-event@14.0.0-beta`](user-event/intro.mdx) instead, as it includes important bug fixes and new features.  
 
 ## Installation
 

docs/user-event/intro.mdx

@@ -13,7 +13,7 @@ if they should be deemed necessary in the light of feedback we receive for this
 All planned breaking changes are already implemented though.  
 If you are starting or actively working on a project,
 we recommend to use this pre-release, as it includes important bug fixes and new features.  
-You can find the docs for `user-event@13.5.0` [here](../ecosystem-user-event).
+You can find the docs for `user-event@13.5.0` [here](../ecosystem-user-event.mdx).
 
 While most examples with `user-event` are for `React`, the library can be used
 with any framework as long as there is a DOM.