Add example session.data structure for labjack acq process

[BrianJKoopman]

Description

See title.

Motivation and Context

I needed this structure documented for writing code in sorunlib, so I grabbed and reduced this example from a running labjack agent at site.

How Has This Been Tested?

Docs change only, based on in field agent.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.