Add a CA Procurement Playbook

[mgifford]

Add a playbook page for procurement officers.

Initial draft (internal) is here: https://docs.google.com/document/d/11l1XiqKOQaioOLbLpgCAU7JlFILHvlsfJjk0-Jqk2JY/edit

• [x] Draft document
• [ ] Vet as Procurement Parker
• [ ] Run by Keith & Mary
• [ ] Talk to DITAP Team
• [ ] Blog about it