Basic Add a pallet tutorial

[JoshOrndorff]

We currently have a thorough and comprehensive tutorial teaching how to add the contracts pallet to the node. That is quite a complex pallet with many associated types, and an RPC that must be wired all the way through the runtime and the node. That tutorial is excellent for learners who are at that level.

We should add another tutorial that teaches how to add a simpler pallet to the runtime. Some good candidates might be:

• Identity
• Collective
• Nicks
• Recovery
• Something from recipes
• Something from ORML