update role doc according to new feature

backend/doc/roles.md

 | invite user to tracim         |  no         | yes, if manager of a given workspace         | yes     |
 |-------------------------------|-------------|-------------|---------|
 | set user global profile rights|  no         | no          | yes     |
-| deactivate user               |  no         | no          | yes     |
+| activate/deactivate user      |  no         | no          | yes     |
+  delete user/ undelete user    |  no         | no          | yes     |
 |-------------------------------|-------------|-------------|---------|
 | access to all user data (/users/{user_id} endpoints) |personal-only|personal-only| yes     |