README doesn't describe the current project

[kanzure]

The README is falling behind. The current README is a leftover from pokecrystal/extras/README.md back when everything was shoved into the extras/ path in pokecrystal.

Things the README should include:

• installation via pip
• use of pokemontools in pokered and pokecrystal
• use of pokemontools outside of pokered/pokecrystal
• organization of the project
• how to run the tests
• licensing status
• calling preprocessor
• calling gbz80disasm

[zachlatta]

👍