chorer: add note about babel config to upgrade guide (#12724)

Author: SimenB

docs/UpgradingToJest28.md

@@ -7,7 +7,7 @@ Upgrading Jest from v27 to v28? This guide aims to help refactoring your configu
 
 :::info
 
-See [changelog](https://github.com/facebook/jest/blob/main/CHANGELOG.md) for the full list of changes.
+See [changelog](https://github.com/facebook/jest/blob/main/CHANGELOG.md#2800) for the full list of changes.
 
 :::
 
@@ -43,6 +43,10 @@ The `testURL` option is removed. Now you should use [`testEnvironmentOptions`](C
 + }
 ```
 
+### Babel config
+
+`babel-jest` now passes `root: config.rootDir` to Babel when resolving configuration. This improves compatibility when using `projects` with differing configuration, but it might mean your babel config isn't picked up in the same way anymore. You can override this option by passing options to `babel-jest` in your [configuration](Configuration.md#transform-objectstring-pathtotransformer--pathtotransformer-object).
+
 ## Fake Timers
 
 Fake timers were refactored to allow passing options to the underlying [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers).