Add v1.5 settings locations to docs

[Kissaki]

As @Krzmbrzl mentions in this comment the settings location changes in Mumble 1.5. (Mumble 1.5 is currently in Release Candidate state).

We need to add this information to the settings storage location user docs. (hugo/content/documentation/user/settings-storage-location/index.md)

This should include the settings location for 1.5 onwards, where we always save the settings as a JSON file, regardless of the OS we're on.
I just don't know the locations of other OS than linux by-heart right now.

mumble-voip/mumble@e828ef0/src/mumble/Settings.cpp#L1273-L1273

or rather

mumble-voip/mumble@e828ef0/src/mumble/Settings.cpp#L1310-L1318