Document how to permit a wildcard IP on device-server

[wvteijlingen]

According to this thread on together you can add a wildcard IP to a device-server by using a *.

(...) it is possible to create a wildcard key if you populate the permitted_ips with the current IP you're making calls from and * to also add wildcard.

This information is critical when you're dealing with dynamic IPs (which is most of the time I think). Therefore I think this information should be added to the documentation.

[OGKevin]

@wvteijlingen thanks for reporting. As this is a simple text addition, feel free to create a PR adding this to DESCRIPTION.MD.

[wvteijlingen]

#72