Clarify more concisely how concepts relate to each other

[itowlson]

Fixes #59.

[kate-goldenring]

At first glance, i thought this acted almost as a table of contents; however, as it references non-design pages, this should maybe live elsewhere

[rylev]

@itowlson @kate-goldenring should this be rebased/merged or closed?

[kate-goldenring]

I think we should still add this in as a TOC for the design section. This needs to be rebased, filenames updated, and this added to summary.md such that it is the top level for the "Understanding the Component Model" section

[kate-goldenring]

@itowlson can we revisit this and see if we can fit in this glossary? It is a great overview for someone who is learning what WASI, WIT and the component model are. I think the package, world, and interface definitions are already covered in the WIT explainer but having a TLDR of them somewhere (maybe the top of the WIT document) could be helpful.