Add a section on building a community, with resources

[FokkeZB]

More of a soft-topic, but could well be part of the refactored structure.

Resources:

• Presentation: https://docs.google.com/a/thethingsindustries.com/presentation/d/1v9cwygSAAx4m0lXMRZisfo2S7iYtxB4tpwRQK5R5Ttc/edit?usp=sharing (more on Google Drive)