Contribution guidelines

Install/update the dependencies:
```
npm i
```
Make sure all of the tests pass:
```
npm t
```
Make sure the code lints:
```
npm run lint
```
Adhere to the coding conventions that are used elsewhere in the codebase.
New code must have new unit tests.
New features or changes to existing features must be documented in the readme file.
Add yourself to the authors file.