(DRAFT) Proposed updates to UnixFS section

[ElPaisano]

PR Summary:
Updates to https://docs.ipfs.tech/concepts/file-systems/#unix-file-system-unixfs

Depends on ipfs/specs#331 (WIP)

Updates:

• At beginning of section, adds a summary of what happens when a file is imported
• Links to each module section (Data Formats, Importer, Exporter)
• Restructures Data Formats section to use tables
• In the Importer section, describes the purpose of chunking
• Reformats large chunks of texts into lists in Chunking and Layout sections
• general, updates formatting, grammar and structure

Todos:

• Review this with @TMoMoreau for style and writing stuff. The styling here is probably inconsistent and could use second opinion / eyes
• Review with IPFS engineers (???) for tech. Specifically, I need feedback on some things that I might have incorrectly assumed were implied, as well as additional input on the data format fields, the chunking process, and the layout process.

Sidebar:
It might make sense to break this section into "functional" and "conceptual" parts. The "functional" content would included things like technical specs, implementation specifics, example code, "how to do XYZ with js-ipfs-unixfs", etc and the "conceptual" part could describe the data format, serialization/deserialization, import and export. Alot of that info is already on this page / in other parts of the IPFS docs, but I think that separating such info and reorganizing it would help with readability and info overload. This is sort of what I attempted here. That might be out of scope for this PR, but figured I'd mention it.

[lidel]

fysa proper UnixFS specs are being created in ipfs/specs#331 – may be a good idea to park technical review until we finish basic spec work