Add acmcsuf.com/roadmap documentation

[EthanThatOneKid]

What's your idea?

Documentation is needed to explain the way that our public product roadmap https://acmcsuf.com/roadmap is used, enabling it or systems like it to be used in the future.

The documentation could either be in the form of a blog post or a new wiki article.

[EthanThatOneKid]

Related art:

• https://github.com/github/roadmap