[#150] .gitignore Nanoc's crash log.
[#150] Mention the RVM 2 presentation.
[#150] Contribution should mention HACKING.md
[Closes #150] Remove Passenger 2 instructions.

Phusion prefers people use Passenger 3, so push them in that direction.
Merge pull request #151 from rvm/150-content_updates

[Closes #150] Content updates.