docs: add tips for working with commitlint

- Commit title starting with `feat: ` trigger a minor version bump

- Commit body contains `BREAKING CHANGE: ` trigger a major version bump. This can be part of commits of any _type_.

### Tip: Test commit messages locally

Testing the commit message locally can speed up the iteration cycle. It can be configured as follows:

``` sh

# install dev dependencies, if necessary

npm install

# usage

npx commitlint --from=master # if targeting latest

npx commitlint --from=1.x # if targeting 1.x stable

```

### Tip: Use a git hook with commitlint

To save yourself the manual step of testing the commit message, you can use a commit hook.

At the root of this project, add `.git/hooks/commit-msg` with the following contents:

``` sh

#!/bin/sh

npx commitlint --edit

```

Then, run `chmod +x .git/hooks/commit-msg` to make it executable.

## Automatic versioning

Each push to `master` triggers a [`semantic-release`](https://semantic-release.gitbook.io/semantic-release/)