Add context description to clarify purpose of this resource

[yetanothertw]

This quick reference would benefit from a description that explains its purpose, for example that it describes the technical implementation of various style elements.

For information about stylistic choices, see the IBM Style Guide and the Red Hat supplementary style guide for product documentation (https://redhat-documentation.github.io/supplementary-style-guide/#user-replaced-values)

For information about modular documentation guidelines, see the Modular Documentation Reference Guide (https://redhat-documentation.github.io/modular-docs/).