Initialize project management documentation

[jeancochrane]

Overview

Add some basic documentation for project management, including:

• Project collateral
• Best practices for working with source control

Closes https://github.com/datamade/how-to/issues/20.

Testing instructions

• View the rendered directory on GitHub: https://github.com/datamade/how-to/tree/feature/jfc/project-management/project-management
• Confirm that the markdown looks good (including links)

[jeancochrane]

Added PR and issue templates! I tried the multiple issue template workflow, we'll see if it works when I pull this in.