Notes for project managers

As we are more than 1 project manager, it would be great if I could make notes somewhere to the project that are only visible for the project managers.

This is important if 1 project manager takes over because somebody is ill or on vacation. If the project manager is then back and would be able to take the projects back again, then mails could be avoided and this project manager would only need to go through the notes made and would know the status already.