Add specification for Web Pathing

[lidel]

This is a placeholder for writing a specification on how /ipfs and /ipns paths are intended to work on HTTP Gateways and other Web contexts, such as ipfs:// and ipns:// in browsers with native, verifiable handler for these schemas.

Initial Scope Idea

• Should be at https://specs.ipfs.tech/web-pathing/ (very important)
• This is not "just" writing down UnixFS pathing. Web Pathing is about defining a MVP subset of IPFS and conventions to ensure interop with the web.
• This is not only about HTTP URLs for Gateways, but will also inform behavior of native ipfs:// and ipns:// (e.g. Brave, ipfs-chromium), which is expected to be the same on both.

Things the specs MUST cover

Moved to #453 ← please comment on the PR.