Document in the README file the available configuration parameters

There are currently many configuration parameters that can be used in order to customize the behavior of the code or even of a specific session or channel. The in virtually most cases, t he "documentation" of these values resides in the code (except for a few select cases that are mentioned in the current markdown documentation).

We need to establish and maintain a table that lists all the available configurations, the behavior they control, their default value, the class that defines them, etc...