Update contributing documentation

[DanielRosenwasser]

@RyanCavanaugh recently walked through CONTRIBUTING.md and our wiki and commented that the process is a bit old and crusty. In the interest of making things more obvious for contributors, we need to clean things up here.

I'm currently trying to get an overview of the project, including contribution etc.

The project-host (github) is not very helpful with this:

• 3891 issues
• 112 Issue-Labels in one(!) level
• zero functionality for "subsystems" or "components"

Any serious issue-tracker for larger projects (like typescript is) has fields for:

• Issue-Category (bug, feature, enhancement, question etc.)
• Severity (on user side)
• Priority (from team)
• most (MOST) important: Component (or Subsystem)

Don't believe this"

Test:

• Focus on the "compiler" subsystem within the typescript code.
• Get notifications ONLY for src/compiler subsystem.
• Follow Issues for the "compiler" subsystem.

=> you can't, because Github does not support this.

Why? Because the early Gihub-product-managers had "flat" thinking, and the masses were fine with it.

An excellent system needs zero documentation, because it's self-documenting.

But! A system full of weaknesses and flaws needs many documentation.

Fix those very fundamental github weaknesses, then start to write contributor-documentation.

4000 issues, 113 labels, seriously, you don't see the usability disaster here?

.