Final mods for initial CONTRIBUTING.md

There are still a few sections that need to be written or expanded on.
I like the more compact format for two reasons:
- I believe that the code structure information is conveyed to humans through indenting, not braces (the existence of Python is support for that idea)
- I like my screens to have a high code density and resent the wasted line(s) of other curly formatting methods

However, great minds can disagree on this and many other coding style questions!