Add announcement link

Author: Link-

packages/cache/README.md

@@ -18,7 +18,7 @@ If you do not upgrade, all workflow runs using any of the deprecated [@actions/c
 
 Upgrading to the recommended version should not break or require any changes to your workflows beyond updating your `package.json` to version `4.0.0`.
 
-Read more about change & access the migration guide: [reference to the announcement](TBD).
+Read more about the change & access the migration guide: [reference to the announcement](https://github.com/actions/toolkit/discussions/1890).
 
 ## Usage
 

packages/cache/RELEASES.md

@@ -14,7 +14,7 @@ If you do not upgrade, all workflow runs using any of the deprecated [@actions/c
 
 Upgrading to the recommended version should not break or require any changes to your workflows beyond updating your `package.json` to version `4.0.0`.
 
-Read more about change & access the migration guide: [reference to the announcement](TBD).
+Read more about the change & access the migration guide: [reference to the announcement](https://github.com/actions/toolkit/discussions/1890).
 
 #### Minor changes