add a portal to xen addon

thanks

cool

can confirm we are working on Gog'Noks Xen Map Essentials 2, the best map in Gmod history.

These are quite outdated map materials, these were exported from the very first version of the Beta Black Mesa Xen Maps released to the public, so alot of missing textures will be present in some areas, there may be some other workshop apps that add the more recent exports I believe.

Some of the blend textures are missing their other half, still tho glad somebody uploaded some Xen map materials.