Add section on user management (#5)

scenario-databases.rst

@@ -6,6 +6,17 @@ Scenario databases hosted by IIASA
 The *Energy, Climate and Environment* program (ECE) at IIASA is hosting many databases
 for the community to facilitate scenario analysis, model comparison and dissemination.
 
+Permission management
+---------------------
+
+There are public and project-internal (private) databases. Access to project-internal
+instances is managed via the *Scenario Services Manager* at
+https://manager.ece.iiasa.ac.at. To participate in a project, please create an account
+and send the username to the project managers by email.
+
+You can see all public and private database instances to which you have access,
+including your model view/submit/edit permissions, in the *Services* tab of the manager.
+
 Model registration
 ------------------