📝 Update release notes

docs/release-notes.md

@@ -1,5 +1,6 @@
 ## Latest changes
 
+* Add GitHub action [Issue Manager](https://github.com/tiangolo/issue-manager). PR [#742](https://github.com/tiangolo/fastapi/pull/742).
 * Fix typos in docs. PR [734](https://github.com/tiangolo/fastapi/pull/734) by [@bundabrg](https://github.com/bundabrg).
 * Fix usage of `custom_encoder` in `jsonable_encoder`. PR [#715](https://github.com/tiangolo/fastapi/pull/715) by [@matrixise](https://github.com/matrixise).
 * Fix invalid XML example. PR [710](https://github.com/tiangolo/fastapi/pull/710) by [@OcasoProtal](https://github.com/OcasoProtal).