Added a bit of documentation under usage

                       
| Q             | A   |
| ---           | --- |
| Bug fix?      | y   |
| New feature?  | n   |
| BC breaks?    | n   |
| Deprecations? | n   |
| Tests pass?   | y   |
| Fixed tickets | #14 |
| License       | MIT |
| Doc PR        |     |