add setup for mac apple silicon

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.6.5
+FROM --platform=linux/amd64 ruby:2.6.5
 RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
 RUN mkdir /myapp
 WORKDIR /myapp

README.md

@@ -55,6 +55,8 @@ Open your favorite browser, navigate to `http://localhost:3000` and start hackin
 ## Docker Install
 To run Railsgoat with Docker you must first have [Docker](https://docs.docker.com/engine/installation/) and [Docker Compose](https://docs.docker.com/compose/install/) installed. Once those dependencies are installed, cd into the Railsgoat directory where you've cloned the code and run. Rails requires Compose **1.6.0** or above and require a Docker Engine of version **1.10.0** or above.
 
+For Mac Apple Silicon (ARM64) you must also have Rosetta install
+
 ```
 #~/code/railsgoat
 $ docker-compose build