proposal to add Swift Docs repository structure

[heckj]

Adds a proposal that outlines collecting and organizing sets of documentation into a single repository, migrating content from the /articles directory of swift.org into these new collections, and presenting them back through to the website using DocC archives, hosted similarly to a number of other projects.

Motivation:

The documentation for Swift has grown organically since its open source release. That growth has resulted in fragmented locations to find information, little organization, and inconsistencies in updating content as the language grew. The Swift WebSite workgroup started down the path to redesign the swift.org website, and parallel with launched the Swift Information Architecture project, to both revitalize the site and to set a structure that supports further, consistent growth for Swift documentation.

Modifications:

• adds the proposal with the details of the new repository, organization structure, and reviewer mechanisms to support technical accuracy vetted by people delegated from the relevant groups and teams within the Swift community.

Result:

Nothing immediately visible on the site, provides the internal proposal for future reference and implementation.