Update session.data example in main registry process

[BrianJKoopman]

Description

This expands the session.data documentation for the main registry process.

Motivation and Context

Found info in the current session.data didn't match the docs while working on simonsobs/sorunlib#42.

How Has This Been Tested?

Not tested. Docs updates only. Updated session.data was determined on a registry from ocs v0.9.3, but there doesn't appear to be any changes since then.

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.

[jlashner]

Looks good, thanks for updating this!