Create online documentation for accuracy program

Create documentation for the `accuracy` program with:

1. name
2. synopsis
3. description
4. options
5. examples

Create the documentation in `docs/accuracy.md` and link to it from `README.md`!

Addresses #6.

Start by reading the `accuracy` program and the existing `README.md` to understand its usage and documentation style. Create `docs/accuracy.md` with the name, synopsis, description, options, and examples, then link it from `README.md`; the documentation should cover how to use the program.

Written by the indexing model from the issue text.