message: docs(SCSS): spacing() usage docs
diff: # Spacing
  -All spacing should be defined using the `spacing()` helper method. This ensures that all spacings
  -are valid spacings within our design language.
  +All spacing should be defined using the `spacing()` helper method. This ensures that each spacing
  +is a valid spacing within our design language.
  ```scss
  +// Use the default spacing:
  .foo {
  margin-bottom: spacing();
  }
  +// Use a specific spacing:
  +.bar {
  + margin-bottom: spacing(small, 2);
  +}
  +```
  +
  +## Available spacing options
  +
  +- Small: 12, 8, 4
  +- Base: 16
  +- Large: 24, 32, 40, 48, 56, 72, 96
  +
  +You can access each option using zero-based indexes:
  +
  +```scss
  +spacing() // 16px
  +// (for the first space in a collection we can omit the second parameter)
  +spacing(small) // 12px
  +spacing(small, 2) // 4px
  +spacing(large) // 24px
  +spacing(large, 4) // 56px
  ```
  +
  +Passing in an invalid spacing will throw a Sass compile error.
  