Bring back "Resources" section to gh-pages

[onebree]

Self-explanatory. This will also help to close a couple PRs.

[akz92]

This would be great. I was taking a look at the old "Resources" section and some of the links are dead, maybe we could come up with a new list of up-to-date articles/videos and use them on the new section.

These are some of the current ones that are worth keeping IMO:

Everyday Rails Testing with RSpec
thoughtbot's RSpec Related Reading
Don't make your code "More Testable"
Pluralsight's Testing Ruby Applications with RSpec

I believe we don't need to add links to official documentations as those are pretty well-known resources. Also, maybe linking to other people's best-practices seems counter productive as in theory if they've talked about something that we're not covering maybe we should add a new section about it.