Add Semantic Version Policy from stylelint about stylelint-config-standard HOT 3 CLOSED

## Semantic Versioning Policy

stylelint-config-standard follows [semantic versioning](http://semver.org). However, due to the nature of stylelint as a code quality tool, it's not always clear when a minor or major version bump occurs. To help clarify this for everyone, based on stylelint's [semantic versioning policy](https://github.com/stylelint/stylelint#semantic-versioning-policy) which is in turn based on ESLint's [semantic versioning policy](https://github.com/eslint/eslint#semantic-versioning-policy), we've defined the following subset of stylelint's semantic versioning policy for stylelint-config-standard:

-   Patch release (intended to not break your lint build)
    -   A bug fix in a rule that results in stylelint reporting fewer errors.
    -   Improvements to documentation.
    -   Non-user-facing changes such as refactoring code, adding, deleting, or modifying tests, and increasing test coverage.
    -   Re-releasing after a failed release (i.e., publishing a release that doesn't work for anyone).

-   Minor release (might break your lint build)
    -   A bug fix in a rule that results in stylelint reporting more errors.
    -   A new rule is added.
    -   A new option to an existing rule that does not result in stylelint reporting more errors by default.
    -   An existing rule is deprecated.

-   Major release (likely to break your lint build)
    -   A change in the documented behaviour of an existing rule results in stylelint reporting more errors by default.
    -   An existing rule is removed.

According to our policy, any minor update may report more errors than the previous release (ex: from a bug fix). As such, we recommend using the tilde (`~`) in `package.json` e.g. `"stylelint": "~7.2.0"` to guarantee the results of your builds.