Docs: Changelog: Emphasize upgrade guide

Author: jaredbeck

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## 3.0.0
 
+Please read the [guide on migrating from CanCanCan 2.x to 3.0](https://github.com/CanCanCommunity/cancancan/wiki/Migrating-from-CanCanCan-2.x-to-3.0)
+
 * [#560](https://github.com/CanCanCommunity/cancancan/pull/560): Add support for Rails 6.0. ([@coorasse][])
 * [#489](https://github.com/CanCanCommunity/cancancan/pull/489): Drop support for actions without a subject. ([@andrew-aladev][])
 * [#474](https://github.com/CanCanCommunity/cancancan/pull/474): Allow to add attribute-level rules. ([@phaedryx][])
@@ -14,8 +16,6 @@
 * [#568](https://github.com/CanCanCommunity/cancancan/issues/568): Automatically freeze strings in all files. ([@coorasse][])
 * [#577](https://github.com/CanCanCommunity/cancancan/pull/577): Normalise rules traversing associations to reduce the number of joins. ([@coorasse][])
 
-Please read the [guide on migrating from CanCanCan 2.x to 3.0](https://github.com/CanCanCommunity/cancancan/wiki/Migrating-from-CanCanCan-2.x-to-3.0)
-
 ## 2.3.0 (Sep 16th, 2018)
 
 * [#528](https://github.com/CanCanCommunity/cancancan/issues/528): Compress irrelevant rules before generating a query to optimize performances. ([@coorasse][])