Added note about memory management of passed in strings to Dart_SetVMFlags.
Added note about memory management of passed in strings to Dart_SetVMFlags.

Change-Id: I6eb20034ba4812fa4cdd288d326836637664439b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/130725
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Commit-Queue: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk