Documentation for required components in loading entities

[gsantia]

When working with the load stage in isolation it took some time to get the data I wanted to be loaded into the standardized form. I was working off of the Data Service documentation, which not only seems to be incorrect sometimes, but can lead to ambiguities. For example, which type of ID is really needed when it refers to an entity ID attribute (external or kf_id)? Or, how exactly should the values be formatted (such as with genomic-file.hash, there's no indication given). Another concern here is having to take entities found in the Data Service and find their appropriate counterparts in the concepts.py file.

The Kids First Data Service target API plugin .py file is much more precise in what attributes are required for each entity using the load stage. But checking this file wasn't immediately apparent to me, and it might be better to have this information in a more user-friendly format in the documentation. Not only would this make using the load stage in isolation more straight-forward, but I could see it making using the ingest library easier for people not already familiar with it.

This could also be interpreted as an issue with the Data Service documentation. I know that the ingest library is designed for use with multiple target API plugins.