[config][docs] Updating configuration and adding a guide.

CHANGELOG
=========
- Added `config/README.md` to explain the use case for each
  configuration file.
- Added `config/local_cluster_scheduler.yml` and
  `config/local_cluster_asset_dev.yml`.
- Removed asset overrides from all configuration files except for
  `config/local_cluster_asset_dev.yml`.
Merge pull request #10 from airbnb/configs

[config][docs] Updating configuration and adding a guide.