Adding to "customize/sass/#add-to-map" info about utilities

Created by: bachelorcthulhu

Description

Added example of generating utilities with custom colors, that user added to map. Also added reference to "Color" page - where is located explanation of utilities and another example

Motivation & Context

At adding new colors to map, there will be available only bg-custom-color and link-custom-color classes. Right now, that page has no information about adding new classes and utilities, so user maybe confused, why he can't use custom color to background.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• All new and existing tests passed

Live previews

https://deploy-preview-37319--twbs-bootstrap.netlify.app/docs/5.2/customize/sass/#add-to-map