Add description tag

A description tag for every op and each parameter of the op would be useful. Maybe this descriptions can be used to auto-generate the java-doc of the namespace methods.

The issue does not name files, tests, or an entry point. Start by locating how ops and their parameters are declared, then determine how descriptions would be represented and consumed for generated JavaDoc; done requires coverage for every op and parameter and a clear generation workflow.

Written by the indexing model from the issue text.