Setting Permissions by namespace
To set namespace permissions, you need the operator role.
You can set the edit rights for each of the three namespaces: Setting, Notes and Rules. For example, you can limit the editing of the Rules to only Storytellers, or enable everyone to edit the Notes namespace.
Note that at this time, you can only set who can edit a namespace: you cannot limit who is able to see a namespace. Thus, it is probably best not to keep secret DM notes in the Notes namespace.
Where to set the namespace permissions
The namespace permissions can be configured in the main campaign configuration. Click the cogwheel in the top right corner. If the cogwheel is not visible, make sure you are logged in, are a member of the campaign and have Operator permission for the campaign.
Once in the configuration overview, pick the Wiki Settings item. The header Wiki Edit Rights has three boxes for Setting Edit Rights, Rules Edit Rights and Notes Edit Rights.
By default, each namespace is writable by everyone. If you want to restrict a certain namespace, check the box, and you can set which roles (game masters, moderators or engineers) can edit the namespace. Operators can always edit each namespace.
You can also grant access to specific players regardless of their role, using the Allowed players section where you can manually add players by name. Note that you have to update the campaign configuration before any changes you make take effect.