docs: v0.13 migration notes

docs/abra/upgrade.md

@@ -53,6 +53,15 @@ And test things work.
 
 > General release notes are [here](https://git.coopcloud.tech/toolshed/abra/releases/)
 
+### `0.12.x-beta` -> `0.13.x-beta`
+
+* `abra recipe sync` went away. You now only need to run `upgrade`/`release`.
+  See [`#682`](https://git.coopcloud.tech/toolshed/abra/issues/682) for the
+  design details and
+  [here](/maintainers/handbook/#upstream-released-a-new-version-how-do-i-upgrade-the-recipe)
+  for the revised documentation. Thanks to `@iexos` for getting this out the
+  door!
+
 ### `0.11.x-beta` -> `0.12.x-beta`
 
 * `kadabra` has been archived and is no longer published alongside `abra`