Adding Steam Deck built process

[vitormmatos]

It is indeed possible to build the game for Steam Deck.
I've done it, and works greatly. I think it would be great to add it to the wiki.

I forked the project and added some instructions on how to, it can be checked on the link below: https://github.com/vitormmatos/sm64plus/wiki/Manual-Building-Guide#steam-deck