Replaced config w/ dotenv. Hydrate docker nginx using env. Updated readme

docker-entrypoint.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+set -eu
+
+export SEASONED_API=${SEASONED_API:-http://localhost:31459}
+export SEASONED_DOMAIN=${SEASONED_DOMAIN:-localhost}
+
+envsubst '$SEASONED_API,$SEASONED_DOMAIN' < /etc/nginx/conf.d/default.conf.template > /etc/nginx/conf.d/default.conf
+
+exec "$@"