Address the steps a state entity needs to take if it wants to reuse existing code

[lukefretwell]

via @mannyb16:

Although the Open Source Policy addresses (i) code re-use and (ii) code redistribution, the Playbook focuses on code redistribution but does not address the steps a state entity needs to take if it wants to reuse existing code.

• add to playbook: https://codecagov-playbook.readthedocs.io/en/latest/README/
• add to doc: https://docs.google.com/document/d/1hXYzV_KW49epVuj9EuUGP1hNNARRMf_yVi1Uz5XX_oI/edit?usp=sharing