Document relocation of PUB_CACHE.

See: #52386
Change-Id: I48149aeeea5a78ea2c1d9d7b3b9df8d48ed2310e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/303321
Reviewed-by: Alexander Thomas <athom@google.com>
Auto-Submit: Jonas Jensen <jonasfj@google.com>
Commit-Queue: Jonas Jensen <jonasfj@google.com>

CHANGELOG.md

@@ -528,6 +528,11 @@ using Dart version 2.19, before upgrading to Dart version 3.0.
 - `dart pub get` and related commands will now by default also update the
   dependencies in the `example` folder (if it exists). Use `--no-example` to
   avoid this.
+- On Windows the `PUB_CACHE` has moved to `%LOCALAPPDATA%`, since Dart 2.8 the
+  `PUB_CACHE` has been created in `%LOCALAPPDATA%` when one wasn't present.
+  Hence, this only affects users with a `PUB_CACHE` created by Dart 2.7 or
+  earlier. If you have `path/to/.pub-cache/bin` in `PATH` you may need to
+  update your `PATH`.
 
 ## 2.19.6 - 2023-03-29