Add links from IPFS & IPLD docs & websites to ProtoSchool

[terichadbourne]

Need to review the documentation that exists on IPFS / IPLD sites for topics already covered by ProtoSchool tutorials and link to ProtoSchool where appropriate. This will be primarily in IPFS Files API and IPFS DAG API documentation.

[terichadbourne]

@alanshaw I've put in PRs to link from the DAG API and Files API docs, as well as the summary of all the APIs. (See above for links to those PRs in relevant repos.) Can you think of other spots in current docs where either API is explained that should be updated as well?

[terichadbourne]

@mikeal I added a PR to IPLD to include links to relevant ProtoSchool tutorials on the IPFS DAG API, but I don't have any rights in that repo so wasn't able to tag you as a reviewer. Mind taking a look? ipld/ipld#77

Please let me know if you can think of other spots across IPLD repos where such links would be appropriate (I already added to IPFS DAG API docs).

[alanshaw]

What about linking to protoschool from ipfs.io and js.ipfs.io?