Update Homepage to be a succinct intro/summary page

[mjherzog]

The Home page should:

• Introduce Package-URL as an open source community that promotes practical standards for identifying software across software supply chains.
• Explain the relationship between PURL and VERS.
• Provide an introduction/summary of the website, its major sections and how to use them.

Some specific topics to cover are:

• What is a package? --> redirect discussion to software identifiers / starting with "packages"
• PURL and VERS use cases
• Synergy between PURL and VERS
• Relationship of PURL/VERS

We should also move the Specifications and Tools sections to a new top-level menu item / page because we already have 5 scroll pages for Specs and Tools. A separate page should also make it easier for external reference links because it will not be on the Homepage which is configured differently in Docusaurus from other pages.

[mjherzog]

Starting by replacing the current intro text which is a copy of https://www.packageurl.org/docs/purl/purl-spec-introduction
to a more general summary that also talks about VERS.
See

• Update HomeInfo.mdx #94