Add .editorconfig and contributing.md files

[joshcummingsdesign]

To keep consistency, we should add these two files with some sort of code of conduct like so:

1. All PRs should be related to existing issue, and mention issues that PR is going to be fixing
2. Configure your IDE to use EditorConfig
3. Work in progress commits should be squashed before submitting PR
... and so on...

Something like that