QMSAPI: add path to SourceDocumentsFolder

[#1]

How do I use the QMSAPI to use a string containing say "C:\mystuff\mysources" to add a new path to the list of Source Document Folders used by QDS?

I can get  list of the current folders with

  List<DocumentFolder> sourceDocumentsFolders =

     apiClient.GetSourceDocumentFolders(

        qdsServices[0].ID,

        DocumentFolderScope.General | DocumentFolderScope.Services);

How do I create a DocumentFolder object so that I can to

  soureceDocumentFolders.Add( ...)

And then I assume there is some sort of SaveSettings I need to do.