Move entrypoint based on rails convention

bin/docker-entrypoint.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+set -e
+
+# Remove a potentially pre-existing server.pid for Rails.
+rm -f /usr/src/app/tmp/pids/server.pid
+
+echo "bundle install..."
+bundle check || bundle install --jobs 4
+
+# Then exec the container's main process (what's set as CMD in the Dockerfile).
+exec "$@"