message: [docs] adding notes on the Public role
diff: @@ -50,6 +50,17 @@ The ``sql_lab`` role grants access to SQL Lab. Note that while ``Admin``
  users have access to all databases by default, both ``Alpha`` and ``Gamma``
  users need to be given access on a per database basis.
  +Public
  +""""""
  +It's possible to allow logged out users to access some Superset features.
  +
  +By setting ``PUBLIC_ROLE_LIKE_GAMMA = True`` in your ``superset_config.py``,
  +you grant public role the same set of permissions as for the GAMMA role.
  +This is useful if one wants to enable anonymous users to view
  +dashboards. Explicit grant on specific datasets is still required, meaning
  +that you need to edit the ``Public`` role and add the Public data sources
  +to the role manually.
  +
  Managing Gamma per data source access
  -------------------------------------
  