explicitly indicate that a data source can be set private by curators

doc/permissions.rst

@@ -77,6 +77,7 @@ of a curator is to keep naming between viruses, hosts coherent, but also edit da
  * Edit the :term:`viruses <virus>` and :term:`hosts <host>`
  * Edit the information of a :term:`data source` (except the the list of viewer/editor)
  * Edit the mapping
+ * Switch a :term:`data source` back to private (but not the opposite)
 
 Although, an curator cannot: