feat(docker): readme for docker use

Author: kingsodigie

docker/Dockerfile

@@ -2,5 +2,4 @@
 FROM ruby:2.7-rc
 
 #Install Ruby SDK
-RUN gem install ibm_watson
-
+RUN gem install ibm_watson

docker/README.md

@@ -0,0 +1,19 @@
+## Docker
+You can use docker to test issues you have with the SDK.
+
+1. Install docker
+    - Mac: https://docs.docker.com/docker-for-mac/install/ 
+    - Windows: https://docs.docker.com/docker-for-windows/install/
+1. Download the dockerfile for this SDK and edit as needed.
+    - Change the ruby version as needed `FROM ruby:<your-version>`
+        - For valid ruby base images on docker see https://hub.docker.com/_/ruby 
+    - Copy code/file that you wish to test into the dockerfile 
+        - Add line `COPY <src>... <dest>`
+    - Set dockerfile to execute code file 
+        - Add line `CMD [ "<executable>" ]`
+
+    - For more information on dockerfile construction please visit https://docs.docker.com/engine/reference/builder/
+1. Build and run the docker image.
+    - Navigate to docker file directory
+    - To build the docker image run `docker build --tag=<your-tag> .`
+    - To run the docker image run `docker run <your-tag>`