Change README composition and add more information about running

[asgibson]

The current README offers no explanation of anything in the system except:

• creating a Conda environment (doesn't explain why or what to do afterward)
• running unit tests (important but comprises the bulk of the README)
• License and contributor information

Need to add things like how to:

• write a config.ini file
• write a plugin
• run

Additionally, information about system flow.