TODO: gravyvalet code docs

how-to/local_setup_with_osf.md

with gravyvalet docker-compose.yml
with osf.io docker-compose.yml
without docker?

how-to/new_imp_interface.md

defining interface with operations
required adds to addon_service

how-to/migrating_osf_addon_to_imp.md

implementing imp
current limitations

how-to/new_storage_imp.md

implementing imp
required changes to waterbutler? (with mention of ideal "none")

how-to/key_rotation.md

credentials encryption overview
secret and prior secrets
scrypt configuration