Docs: include a section about permissions that are not assigned by default

[0xGabi]

These permissions are important for those that would like to update Tao Voting settings.

Example of decision vote that creates the permissions and updates the settings: https://gardens.1hive.org/#/xdai/garden/0xb25f0ee2d26461e2b5b3d3ddafe197a0da677b98/vote/2