Change resource.AddFile -> resource.AddWorkshop

[charitea]

This PR changes the resource.AddFile function to resource.AddWorkshop. Currently the .property files aren't downloaded for clients, and servers not using FastDL don't have clients download the logo file when using the resource.AddFile method, so resource.AddWorkshop allows for clients to get both the logo & .property files.

[Cherry]

Thank you for the PR! I've a few questions since I've been out of the gmod sphere for a while, so forgive any ignorance:

• How does this work for folks that don't install the addon via the workshop, and say, customise the logo?
• Or when in local development? Does this prevent the local files from being used, since it's now just pulling from the live workshop version?

[charitea]

• Currently, this would override any custom logo, but right now the logo isn't even being loaded anyway.
• Local files override what's being pulled from the workshop.

[Cherry]

Thanks