XML add-on install method for P3D v4

For the PNW AI ferry system:

I have now implemented the xml add-on installation method for P3D v4.x, with thanks to Roger for checking the xml file. I have amended the PDF instructions (AI Ferry System for Southern BC and Puget Sound v2.pdf) in the download link with a description of the procedure. It’s really pretty simple which should help non-native English speakers.

I would recommend that current users stick with their current installation method provided it is working. If you want to use the new xml method you would have to very carefully disable or remove all files from the current installation so as not to create active duplicate files.