Add useful Resources links

[justinclift]

We should probably include a "Useful Resources" page, along with matching "Resources" URL on our page footer pointing to it.

It'll point to various useful related projects. eg:

• https://datahub.io - Might be interesting to bulk import this too :wink:
• https://opendatacommons.org/licenses
• https://okfn.org
• http://dataportals.org
• https://theodi.org