links between docs versions

[benmccann]

It would be helpful for people who come across the old docs via search engines, etc. to have pointers between the docs versions

E.g. https://oslo.js.org/reference/encoding/ could say something like:

Note that these are the docs for oslo. A newer @oslojs/encoding is available.

Perhaps the https://www.npmjs.com/package/oslo readme could be updated to mention the @oslojs packages? And maybe it should even be deprecated?