feat: added transition changes link

Author: NataliaTepluhina

Diff for: src/guide/migration/introduction.md

@@ -40,9 +40,7 @@ The following consists a list of breaking changes from 2.x:
 - [`$scopedSlots` property is removed and need to be replaced with `$slots`](/guide/migration/slots-unification.html)
 - [Attributes coercion strategy changed](/guide/migration/attribute-coercion.html)
 - [Custom directive API changed to align with component lifecycle](/guide/migration/custom-directives.html)
-- Some transition classes got a rename:
-  - `v-enter` -> `v-enter-from`
-  - `v-leave` -> `v-leave-from`
+- [Some transition classes got a rename](/guide/migration/transition.md)
 - [Component watch option](/api/options-data.html#watch) and [instance method `$watch`](/api/instance-methods.html#watch) no longer supports dot-delimited string paths, use a computed function as the parameter instead
 - In Vue 2.x, application root container's `outerHTML` is replaced with root component template (or eventually compiled to a template, if root component has no template/render option). Vue 3.x now uses application container's `innerHTML` instead.