add registration mode setting

docker-compose.yml

@@ -9,6 +9,8 @@ services:
       DATABASE_URL: "ecto://postgres:postgres@cannery-db/cannery"
       # generate a random base64 string 64 characters long, preferably not from a website
       SECRET_KEY_BASE: "change-me-to-something-random-this-is-really-important-change-it"
+      # uncomment enable sign ups, watch for spam!
+      # REGISTRATION: "public"
     ports:
       # do not expose this publically!
       # always host from behind a reverse proxy with a properly configured certificate