Documentation: add user guide on "configuration" + Hamilton

**Is your feature request related to a problem? Please describe.**
At some point, configuration, i.e. data that shapes the dataflow, or is used as input to the dataflow, needs to get to Hamilton some how.

In some circles this is a YAML file, in others it's code, in others it's command line arguments, etc.

We don't have a prescribed path to do this -- users would like our thoughts here.

**Describe the solution you'd like**
We should have a user guide on this, that includes an example.

It should cover the following scenario that I think covers 80% of cases:

1. Loading configuration for a staging vs production environment. e.g. table names, DB connection info.

There are few ways to do this, so we should show:

1. how to do it with modules & code.
2. how to do it by reading some YAML file.
3. Some decorator constructs that can help.

This should then link to an example.

**Describe alternatives you've considered**
N/A

**Additional context**