Add note about useBlocker/usePrompt to v5 migration guide

Author: brophdawg11

docs/upgrading/v5.md

@@ -947,8 +947,13 @@ const match = matchPath(
 
 `<Prompt>` from v5 (along with `usePrompt` and `useBlocker` from the v6 betas) are not included in the current released version of v6. We decided we'd rather ship with what we have than take even more time to nail down a feature that isn't fully baked. We will absolutely be working on adding this back in to v6 at some point in the near future, but not for our first stable release of 6.x.
 
+<docs-info>We have since added implementations for [`useBlocker`][useblocker] and [`unstable_usePrompt`][useprompt] that you can use instead of `<Prompt>`</docs-info>
+
 ## What did we miss?
 
 Despite our best attempts at being thorough, it's very likely that we missed something. If you follow this upgrade guide and find that to be the case, please let us know. We are happy to help you figure out what to do with your v5 code to be able to upgrade and take advantage of all of the cool stuff in v6.
 
 Good luck 🤘
+
+[useblocker]: ../hooks/use-blocker
+[useprompt]: ../hooks/use-prompt