Barebones supernova UI

[Mordax]

This issue is to discuss potentially how a basic command line ui supernova would have.

By having a basic UI, we can later discuss and add extra functionality easily beyond just pulling starred repos,
for example searching starred repos by programming language, outputting in a variety of formats, etc.

[0xazure]

Any kind of CLI UI will likely rely heavily on the clap arguments parser introduced in #19, and should be driven heavily by functionality provided by supernova.

This 12 Factor CLI Apps article is also good inspiration and provides guidelines for designing usable CLIs.