CIViC description field terminology inconsistent

The field for capturing human-readable text about an evidence item is stored in the description field in our data model, but is formally described as Statement in docs. This discrepancy can cause confusion to downstream consumers of CIViC content, and I recommend we either change our documentation (preferred) or our data model to align the term used to describe this.

The analogous field in Assertions is description (data model and documentation), and the analogous field in Variants is similarly confusing, called description in our data model and Summary in our documentation.

Start by locating the documentation that describes Evidence items, Assertions, and Variants, then compare its terminology with the stated data-model field names. Done means the preferred documentation change consistently identifies these fields as description rather than Statement or Summary, without changing the data model.