Better documentation for properly adding ltsrc and specsens to tool

If I have my own light source or spectral sensitivities, how do I "install" them so that rawtoaces picks up on them? Obviously I can add them to the data directories, but what is the logic that rawtoaces uses to find a particular camera specsens, for example?

Let's say I have a camera file from a Sony a7S I. The tool does not have specsens for this, but let's say that I do. If I add that json file into the specsens directory, what fields need to be properly formatted for rawtoaces to match the specsens to the camera file?

The logic rawtoaces uses (and thus the required formatting for it to work) needs to be documented for both ltsrc and specsens.

Start by tracing how rawtoaces reads the data directories, especially the specsens directory and the JSON camera data, then compare the lookup logic for ltsrc and specsens. Document the required fields, formatting, and matching rules so users can add custom light sources and spectral sensitivities successfully.

Written by the indexing model from the issue text.