spec: `ipfs:` and `ipns:` URI schemes

[Kubuxu]

As a follow up of ipfs/kubo#1678 (comment) we should have clear specs for those URI schemes, in including web+ prefixed ones.

[lidel]

A year passed, I think this issue should be renamed to have "spec: ipfs:// and dweb:", no? :)

Ref. #139 (comment), #152 (comment)

Thanks! Good catch

[da2x]

Any update on this?

[lidel]

See current consensus at:

• https://github.com/ipfs/in-web-browsers/blob/master/ADDRESSING.md

Mid-term plan is to move it to docs.ipfs.io: ipfs-inactive/docs#91 (comment)
Long-term is to write a spec and add it to this repo

[fulldecent]

This issue can please also include documentation of URLs starting with https://ipfs.io/ipfs/

As per #307