Show how to use the Dockerfile directly

Author: dhh

railties/lib/rails/generators/rails/app/templates/Dockerfile.tt

@@ -1,7 +1,8 @@
 # syntax = docker/dockerfile:1
 
-# Note: This Dockerfile is optimized for production deployment and isn't a good base
-# for development enviroments.
+# This Dockerfile is designed for production, not development. Use with Kamal or build'n'run by hand:
+# docker build -t my-app .
+# docker run -d -p 80:80 -p 443:443 --name my-app -e RAILS_MASTER_KEY=<value from config/master.key> my-app
 
 # Make sure RUBY_VERSION matches the Ruby version in .ruby-version
 ARG RUBY_VERSION=<%= gem_ruby_version %>