improvements to challonge scraper/tournament imports and readme

I made some changes to the challonge scraper which make it a first time run on Windows machine (no path errors due to using os.path.join() for generating URLs.

I also modified the import_tournament script so that if a player was added and determined to be an alias for an already existing player, the correct object ID would be used in the player map.

Finally, I wrote a very quick and dirty getting started section in the readme for the purposes of doing quick power rankings using a local database.