Mention PR #7827 in CHANGELOG.md.

CHANGELOG.md

@@ -35,6 +35,9 @@ TBD
   ```
   [@benjamn](https://github.com/benjamn) in [#7810](https://github.com/apollographql/apollo-client/pull/7810)
 
+- Mutations now accept an optional callback function called `reobserveQuery`, which will be passed the `ObservableQuery` and `Cache.DiffResult` objects for any queries invalidated by cache writes performed by the mutation's final `update` function. Using `reobserveQuery`, you can override the default `FetchPolicy` of the query, by (for example) calling `ObservableQuery` methods like `refetch` to force a network request. This automatic detection of invalidated queries provides an alternative to manually enumerating queries using the `refetchQueries` mutation option. Also, if you return a `Promise` from `reobserveQuery`, the mutation will automatically await that `Promise`, rendering the `awaitRefetchQueries` option unnecessary. <br/>
+  [@benjamn](https://github.com/benjamn) in [#7827](https://github.com/apollographql/apollo-client/pull/7827)
+
 - Support `client.refetchQueries` as an imperative way to refetch queries, without having to pass `options.refetchQueries` to `client.mutate`. <br/>
   [@dannycochran](https://github.com/dannycochran) in [#7431](https://github.com/apollographql/apollo-client/pull/7431)