Need to document that 'JIRA Admins' and 'System Admins' should have 'JIRA Users' permission.

We need to add something like the following for the 'admin' and 'system admin' global permissions here: http://confluence.atlassian.com/display/JIRA/Managing+Global+Permissions.

Note: A fully functioning system admin will require both the 'JIRA System Administrators' permission and the 'JIRA Users' permissions. A user with 'JIRA System Administrators' will be able to login to JIRA without the 'JIRA Users' permissions, however, such a user may not be able to perform all regular user functions (e.g. edit their profile).

This behavior changed as indicated at JRA-16980. We need to have this in the 4.0 docs. We should also put it in the 4.1 docs. We will have to remove the documentation if/when we fix this bug.