Build process

[maximegmd]

It would great if we had a BUILD.md file that covers how to build the project.

[poirierlouis]

I'm actually working on updating dependencies and dev/build workflow for the launcher. I'll first update local README. But yes, a BUILD for the entire project and based on platforms would be great.

[Eager31]

@poirierlouis have u reach to build ?
Got an issue with gamenetworkingsockets dependency