CONTRIBUTING.md doesn't have instructions for how to build surmagic from source

[eegrok]

• [ x] I've read, understood, and done my best to follow the *CONTRIBUTING guidelines.

Problem

I'm trying to figure out how to build surmagic from source, so I can contribute to the project.

Feature Request

Please update CONTRIBUTING.md to outline basic build steps for surmagic from the github repo.

Value to Surmagic

If it were easier to build, more people would help contribute :)