Add design guidelines for hero component

This component needs to be documented with guidelines for usage.

The deliverable is to create a paragraph or two that describes the component and its use, and any other information necessary that its consumer should know.

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**Jira Issue:** [PF-4194](https://redhat.atlassian.net/browse/PF-4194)

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**Jira Issue:** [PF-4409](https://redhat.atlassian.net/browse/PF-4409)