We should redirect old individual package docs to the main Ocean docs

[Alexander Condello]

We have had unified docs for quite a while now (#40 was merged in 2019). We should add redirects from the legacy individual doc pages to the Ocean docs. For instance dwave-system's docs are very out of date.

This could/should coincide with update the individual repo links. I think most of them now link to the unified docs, but perhaps not all. Likewise there are some lingering issues (e.g. #150 that should be resolved).