Mention PR #6221 in CHANGELOG.md.

CHANGELOG.md

@@ -53,6 +53,9 @@
 - **[BREAKING]** Support for the `@live` directive has been removed, but might be restored in the future if a more thorough implementation is proposed. <br/>
   [@benjamn](https://github.com/benjamn) in [#6221](https://github.com/apollographql/apollo-client/pull/6221)
 
+- **[BREAKING?]** Refactor `QueryManager` to make better use of observables and enforce `fetchPolicy` more reliably. <br/>
+  [@benjamn](https://github.com/benjamn) in [#6221](https://github.com/apollographql/apollo-client/pull/6221)
+
 - `InMemoryCache` now supports tracing garbage collection and eviction. Note that the signature of the `evict` method has been simplified in a potentially backwards-incompatible way. <br/>
   [@benjamn](https://github.com/benjamn) in [#5310](https://github.com/apollographql/apollo-client/pull/5310)