Document how to generate data for unit tests

Document how to use the attest-tool for generating unit test data. Needed for #64 and #62. In the short term. This needs to be documented publicly so users can give us meaningful reports and ensure fixes have appropriate coverage.

Start by locating the attest-tool entry point and reviewing issues #64 and #62 for the required unit-test data workflow. Document the public steps for generating data and explain how users can provide meaningful reports and support coverage of fixes.

Written by the indexing model from the issue text.