docs(CHANGELOG): add instance id migration link

Thanks @efstathiosntonas !

Author: mikehardy

CHANGELOG.md

@@ -30,7 +30,7 @@ See [Conventional Commits](https://conventionalcommits.org) for commit guideline
 * Firestore: undefined values throw like firebase-js-sdk now. Use ignoreUndefinedProperties setting 'true' to behave as before
 * AdMob: Removed from upstream SDKs. Stay on v11.5.0 for now if you need AdMob. `@invertase/react-native-admob` package planned with v11.5.0 code
 * ML: APIs removed from upstream SDKs. Migrate to cloud function / auth gateway to cloud APIs, as mentioned in links on ML usage document.
-* Instance ID: APIs removed from upstream SDKs. Use Messaging's getToken() to get tokens, see upstream documentation to migrate if needed
+* Instance ID: APIs removed from upstream SDKs. Use Messaging's getToken() to get tokens, see [upstream documentation to migrate](https://firebase.google.com/docs/projects/manage-installations#fid-iid) if needed
 * Messaging.getToken/deleteToken: scoped token APIs removed from upstream APIs. Remove scopes from API calls. deleteToken() should work on iOS now.