Introduces a draft of development mindset/practices.

:boat:

Anyone up for a content review? I should note that this captures what I think is our ideal self moreso than it describes our real self. Even so, I don't think anything I've written is either unattainable for existing projects or would be cast aside as impractical for the hypothetical project starting tomorrow.

Also, I omitted everything I wrote about tools because I think @tristanoneil covered everything more comprehensively than I. Glossary annotations will follow feedback.